cpython-withatomic / Objects / dictobject.c

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
/* Dictionary object implementation using a hash table */

/* The distribution includes a separate file, Objects/dictnotes.txt,
   describing explorations into dictionary design and optimization.
   It covers typical dictionary use patterns, the parameters for
   tuning dictionaries, and several ideas for possible optimizations.
*/

#include "Python.h"
#include "stringlib/eq.h"


/* Set a key error with the specified argument, wrapping it in a
 * tuple automatically so that tuple keys are not unpacked as the
 * exception arguments. */
static void
set_key_error(PyObject *arg)
{
    PyObject *tup;
    tup = PyTuple_Pack(1, arg);
    if (!tup)
        return; /* caller will expect error to be set anyway */
    PyErr_SetObject(PyExc_KeyError, tup);
    Py_DECREF(tup);
}

/* Define this out if you don't want conversion statistics on exit. */
#undef SHOW_CONVERSION_COUNTS

/* See large comment block below.  This must be >= 1. */
#define PERTURB_SHIFT 5

/*
Major subtleties ahead:  Most hash schemes depend on having a "good" hash
function, in the sense of simulating randomness.  Python doesn't:  its most
important hash functions (for strings and ints) are very regular in common
cases:

  >>> map(hash, (0, 1, 2, 3))
  [0, 1, 2, 3]
  >>> map(hash, ("namea", "nameb", "namec", "named"))
  [-1658398457, -1658398460, -1658398459, -1658398462]
  >>>

This isn't necessarily bad!  To the contrary, in a table of size 2**i, taking
the low-order i bits as the initial table index is extremely fast, and there
are no collisions at all for dicts indexed by a contiguous range of ints.
The same is approximately true when keys are "consecutive" strings.  So this
gives better-than-random behavior in common cases, and that's very desirable.

OTOH, when collisions occur, the tendency to fill contiguous slices of the
hash table makes a good collision resolution strategy crucial.  Taking only
the last i bits of the hash code is also vulnerable:  for example, consider
the list [i << 16 for i in range(20000)] as a set of keys.  Since ints are
their own hash codes, and this fits in a dict of size 2**15, the last 15 bits
 of every hash code are all 0:  they *all* map to the same table index.

But catering to unusual cases should not slow the usual ones, so we just take
the last i bits anyway.  It's up to collision resolution to do the rest.  If
we *usually* find the key we're looking for on the first try (and, it turns
out, we usually do -- the table load factor is kept under 2/3, so the odds
are solidly in our favor), then it makes best sense to keep the initial index
computation dirt cheap.

The first half of collision resolution is to visit table indices via this
recurrence:

    j = ((5*j) + 1) mod 2**i

For any initial j in range(2**i), repeating that 2**i times generates each
int in range(2**i) exactly once (see any text on random-number generation for
proof).  By itself, this doesn't help much:  like linear probing (setting
j += 1, or j -= 1, on each loop trip), it scans the table entries in a fixed
order.  This would be bad, except that's not the only thing we do, and it's
actually *good* in the common cases where hash keys are consecutive.  In an
example that's really too small to make this entirely clear, for a table of
size 2**3 the order of indices is:

    0 -> 1 -> 6 -> 7 -> 4 -> 5 -> 2 -> 3 -> 0 [and here it's repeating]

If two things come in at index 5, the first place we look after is index 2,
not 6, so if another comes in at index 6 the collision at 5 didn't hurt it.
Linear probing is deadly in this case because there the fixed probe order
is the *same* as the order consecutive keys are likely to arrive.  But it's
extremely unlikely hash codes will follow a 5*j+1 recurrence by accident,
and certain that consecutive hash codes do not.

The other half of the strategy is to get the other bits of the hash code
into play.  This is done by initializing a (unsigned) vrbl "perturb" to the
full hash code, and changing the recurrence to:

    j = (5*j) + 1 + perturb;
    perturb >>= PERTURB_SHIFT;
    use j % 2**i as the next table index;

Now the probe sequence depends (eventually) on every bit in the hash code,
and the pseudo-scrambling property of recurring on 5*j+1 is more valuable,
because it quickly magnifies small differences in the bits that didn't affect
the initial index.  Note that because perturb is unsigned, if the recurrence
is executed often enough perturb eventually becomes and remains 0.  At that
point (very rarely reached) the recurrence is on (just) 5*j+1 again, and
that's certain to find an empty slot eventually (since it generates every int
in range(2**i), and we make sure there's always at least one empty slot).

Selecting a good value for PERTURB_SHIFT is a balancing act.  You want it
small so that the high bits of the hash code continue to affect the probe
sequence across iterations; but you want it large so that in really bad cases
the high-order hash bits have an effect on early iterations.  5 was "the
best" in minimizing total collisions across experiments Tim Peters ran (on
both normal and pathological cases), but 4 and 6 weren't significantly worse.

Historical: Reimer Behrends contributed the idea of using a polynomial-based
approach, using repeated multiplication by x in GF(2**n) where an irreducible
polynomial for each table size was chosen such that x was a primitive root.
Christian Tismer later extended that to use division by x instead, as an
efficient way to get the high bits of the hash code into play.  This scheme
also gave excellent collision statistics, but was more expensive:  two
if-tests were required inside the loop; computing "the next" index took about
the same number of operations but without as much potential parallelism
(e.g., computing 5*j can go on at the same time as computing 1+perturb in the
above, and then shifting perturb can be done while the table index is being
masked); and the PyDictObject struct required a member to hold the table's
polynomial.  In Tim's experiments the current scheme ran faster, produced
equally good collision statistics, needed less code & used less memory.

Theoretical Python 2.5 headache:  hash codes are only C "long", but
sizeof(Py_ssize_t) > sizeof(long) may be possible.  In that case, and if a
dict is genuinely huge, then only the slots directly reachable via indexing
by a C long can be the first slot in a probe sequence.  The probe sequence
will still eventually reach every slot in the table, but the collision rate
on initial probes may be much higher than this scheme was designed for.
Getting a hash code as fat as Py_ssize_t is the only real cure.  But in
practice, this probably won't make a lick of difference for many years (at
which point everyone will have terabytes of RAM on 64-bit boxes).
*/

/* Object used as dummy key to fill deleted entries */
static PyObject *dummy = NULL; /* Initialized by first call to newPyDictObject() */

#ifdef Py_REF_DEBUG
PyObject *
_PyDict_Dummy(void)
{
    return dummy;
}
#endif

/* forward declarations */
static PyDictEntry *
lookdict_unicode(PyDictObject *mp, PyObject *key, long hash);

#ifdef SHOW_CONVERSION_COUNTS
static long created = 0L;
static long converted = 0L;

static void
show_counts(void)
{
    fprintf(stderr, "created %ld string dicts\n", created);
    fprintf(stderr, "converted %ld to normal dicts\n", converted);
    fprintf(stderr, "%.2f%% conversion rate\n", (100.0*converted)/created);
}
#endif

/* Debug statistic to compare allocations with reuse through the free list */
#undef SHOW_ALLOC_COUNT
#ifdef SHOW_ALLOC_COUNT
static size_t count_alloc = 0;
static size_t count_reuse = 0;

static void
show_alloc(void)
{
    fprintf(stderr, "Dict allocations: %" PY_FORMAT_SIZE_T "d\n",
        count_alloc);
    fprintf(stderr, "Dict reuse through freelist: %" PY_FORMAT_SIZE_T
        "d\n", count_reuse);
    fprintf(stderr, "%.2f%% reuse rate\n\n",
        (100.0*count_reuse/(count_alloc+count_reuse)));
}
#endif

/* Debug statistic to count GC tracking of dicts */
#ifdef SHOW_TRACK_COUNT
static Py_ssize_t count_untracked = 0;
static Py_ssize_t count_tracked = 0;

static void
show_track(void)
{
    fprintf(stderr, "Dicts created: %" PY_FORMAT_SIZE_T "d\n",
        count_tracked + count_untracked);
    fprintf(stderr, "Dicts tracked by the GC: %" PY_FORMAT_SIZE_T
        "d\n", count_tracked);
    fprintf(stderr, "%.2f%% dict tracking rate\n\n",
        (100.0*count_tracked/(count_untracked+count_tracked)));
}
#endif


/* Initialization macros.
   There are two ways to create a dict:  PyDict_New() is the main C API
   function, and the tp_new slot maps to dict_new().  In the latter case we
   can save a little time over what PyDict_New does because it's guaranteed
   that the PyDictObject struct is already zeroed out.
   Everyone except dict_new() should use EMPTY_TO_MINSIZE (unless they have
   an excellent reason not to).
*/

#define INIT_NONZERO_DICT_SLOTS(mp) do {                                \
    (mp)->ma_table = (mp)->ma_smalltable;                               \
    (mp)->ma_mask = PyDict_MINSIZE - 1;                                 \
    } while(0)

#define EMPTY_TO_MINSIZE(mp) do {                                       \
    memset((mp)->ma_smalltable, 0, sizeof((mp)->ma_smalltable));        \
    (mp)->ma_used = (mp)->ma_fill = 0;                                  \
    INIT_NONZERO_DICT_SLOTS(mp);                                        \
    } while(0)

/* Dictionary reuse scheme to save calls to malloc, free, and memset */
#ifndef PyDict_MAXFREELIST
#define PyDict_MAXFREELIST 80
#endif
static PyDictObject *free_list[PyDict_MAXFREELIST];
static int numfree = 0;

void
PyDict_Fini(void)
{
    PyDictObject *op;

    while (numfree) {
        op = free_list[--numfree];
        assert(PyDict_CheckExact(op));
        PyObject_GC_Del(op);
    }
}

PyObject *
PyDict_New(void)
{
    register PyDictObject *mp;
    if (dummy == NULL) { /* Auto-initialize dummy */
        dummy = PyUnicode_FromString("<dummy key>");
        if (dummy == NULL)
            return NULL;
#ifdef SHOW_CONVERSION_COUNTS
        Py_AtExit(show_counts);
#endif
#ifdef SHOW_ALLOC_COUNT
        Py_AtExit(show_alloc);
#endif
#ifdef SHOW_TRACK_COUNT
        Py_AtExit(show_track);
#endif
    }
    if (numfree) {
        mp = free_list[--numfree];
        assert (mp != NULL);
        assert (Py_TYPE(mp) == &PyDict_Type);
        _Py_NewReference((PyObject *)mp);
        if (mp->ma_fill) {
            EMPTY_TO_MINSIZE(mp);
        } else {
            /* At least set ma_table and ma_mask; these are wrong
               if an empty but presized dict is added to freelist */
            INIT_NONZERO_DICT_SLOTS(mp);
        }
        assert (mp->ma_used == 0);
        assert (mp->ma_table == mp->ma_smalltable);
        assert (mp->ma_mask == PyDict_MINSIZE - 1);
#ifdef SHOW_ALLOC_COUNT
        count_reuse++;
#endif
    } else {
        mp = PyObject_GC_New(PyDictObject, &PyDict_Type);
        if (mp == NULL)
            return NULL;
        EMPTY_TO_MINSIZE(mp);
#ifdef SHOW_ALLOC_COUNT
        count_alloc++;
#endif
    }
    mp->ma_lookup = lookdict_unicode;
#ifdef SHOW_TRACK_COUNT
    count_untracked++;
#endif
#ifdef SHOW_CONVERSION_COUNTS
    ++created;
#endif
    return (PyObject *)mp;
}

/*
The basic lookup function used by all operations.
This is based on Algorithm D from Knuth Vol. 3, Sec. 6.4.
Open addressing is preferred over chaining since the link overhead for
chaining would be substantial (100% with typical malloc overhead).

The initial probe index is computed as hash mod the table size. Subsequent
probe indices are computed as explained earlier.

All arithmetic on hash should ignore overflow.

The details in this version are due to Tim Peters, building on many past
contributions by Reimer Behrends, Jyrki Alakuijala, Vladimir Marangozov and
Christian Tismer.

lookdict() is general-purpose, and may return NULL if (and only if) a
comparison raises an exception (this was new in Python 2.5).
lookdict_unicode() below is specialized to string keys, comparison of which can
never raise an exception; that function can never return NULL.  For both, when
the key isn't found a PyDictEntry* is returned for which the me_value field is
NULL; this is the slot in the dict at which the key would have been found, and
the caller can (if it wishes) add the <key, value> pair to the returned
PyDictEntry*.
*/
static PyDictEntry *
lookdict(PyDictObject *mp, PyObject *key, register long hash)
{
    register size_t i;
    register size_t perturb;
    register PyDictEntry *freeslot;
    register size_t mask = (size_t)mp->ma_mask;
    PyDictEntry *ep0 = mp->ma_table;
    register PyDictEntry *ep;
    register int cmp;
    PyObject *startkey;

    i = (size_t)hash & mask;
    ep = &ep0[i];
    if (ep->me_key == NULL || ep->me_key == key)
        return ep;

    if (ep->me_key == dummy)
        freeslot = ep;
    else {
        if (ep->me_hash == hash) {
            startkey = ep->me_key;
            Py_INCREF(startkey);
            cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
            Py_DECREF(startkey);
            if (cmp < 0)
                return NULL;
            if (ep0 == mp->ma_table && ep->me_key == startkey) {
                if (cmp > 0)
                    return ep;
            }
            else {
                /* The compare did major nasty stuff to the
                 * dict:  start over.
                 * XXX A clever adversary could prevent this
                 * XXX from terminating.
                 */
                return lookdict(mp, key, hash);
            }
        }
        freeslot = NULL;
    }

    /* In the loop, me_key == dummy is by far (factor of 100s) the
       least likely outcome, so test for that last. */
    for (perturb = hash; ; perturb >>= PERTURB_SHIFT) {
        i = (i << 2) + i + perturb + 1;
        ep = &ep0[i & mask];
        if (ep->me_key == NULL)
            return freeslot == NULL ? ep : freeslot;
        if (ep->me_key == key)
            return ep;
        if (ep->me_hash == hash && ep->me_key != dummy) {
            startkey = ep->me_key;
            Py_INCREF(startkey);
            cmp = PyObject_RichCompareBool(startkey, key, Py_EQ);
            Py_DECREF(startkey);
            if (cmp < 0)
                return NULL;
            if (ep0 == mp->ma_table && ep->me_key == startkey) {
                if (cmp > 0)
                    return ep;
            }
            else {
                /* The compare did major nasty stuff to the
                 * dict:  start over.
                 * XXX A clever adversary could prevent this
                 * XXX from terminating.
                 */
                return lookdict(mp, key, hash);
            }
        }
        else if (ep->me_key == dummy && freeslot == NULL)
            freeslot = ep;
    }
    assert(0);          /* NOT REACHED */
    return 0;
}

/*
 * Hacked up version of lookdict which can assume keys are always
 * unicodes; this assumption allows testing for errors during
 * PyObject_RichCompareBool() to be dropped; unicode-unicode
 * comparisons never raise exceptions.  This also means we don't need
 * to go through PyObject_RichCompareBool(); we can always use
 * unicode_eq() directly.
 *
 * This is valuable because dicts with only unicode keys are very common.
 */
static PyDictEntry *
lookdict_unicode(PyDictObject *mp, PyObject *key, register long hash)
{
    register size_t i;
    register size_t perturb;
    register PyDictEntry *freeslot;
    register size_t mask = (size_t)mp->ma_mask;
    PyDictEntry *ep0 = mp->ma_table;
    register PyDictEntry *ep;

    /* Make sure this function doesn't have to handle non-unicode keys,
       including subclasses of str; e.g., one reason to subclass
       unicodes is to override __eq__, and for speed we don't cater to
       that here. */
    if (!PyUnicode_CheckExact(key)) {
#ifdef SHOW_CONVERSION_COUNTS
        ++converted;
#endif
        mp->ma_lookup = lookdict;
        return lookdict(mp, key, hash);
    }
    i = hash & mask;
    ep = &ep0[i];
    if (ep->me_key == NULL || ep->me_key == key)
        return ep;
    if (ep->me_key == dummy)
        freeslot = ep;
    else {
        if (ep->me_hash == hash && unicode_eq(ep->me_key, key))
            return ep;
        freeslot = NULL;
    }

    /* In the loop, me_key == dummy is by far (factor of 100s) the
       least likely outcome, so test for that last. */
    for (perturb = hash; ; perturb >>= PERTURB_SHIFT) {
        i = (i << 2) + i + perturb + 1;
        ep = &ep0[i & mask];
        if (ep->me_key == NULL)
            return freeslot == NULL ? ep : freeslot;
        if (ep->me_key == key
            || (ep->me_hash == hash
            && ep->me_key != dummy
            && unicode_eq(ep->me_key, key)))
            return ep;
        if (ep->me_key == dummy && freeslot == NULL)
            freeslot = ep;
    }
    assert(0);          /* NOT REACHED */
    return 0;
}

int
_PyDict_HasOnlyStringKeys(PyObject *dict)
{
    Py_ssize_t pos = 0;
    PyObject *key, *value;
    assert(PyDict_CheckExact(dict));
    /* Shortcut */
    if (((PyDictObject *)dict)->ma_lookup == lookdict_unicode)
        return 1;
    while (PyDict_Next(dict, &pos, &key, &value))
        if (!PyUnicode_Check(key))
            return 0;
    return 1;
}

#ifdef SHOW_TRACK_COUNT
#define INCREASE_TRACK_COUNT \
    (count_tracked++, count_untracked--);
#define DECREASE_TRACK_COUNT \
    (count_tracked--, count_untracked++);
#else
#define INCREASE_TRACK_COUNT
#define DECREASE_TRACK_COUNT
#endif

#define MAINTAIN_TRACKING(mp, key, value) \
    do { \
        if (!_PyObject_GC_IS_TRACKED(mp)) { \
            if (_PyObject_GC_MAY_BE_TRACKED(key) || \
                _PyObject_GC_MAY_BE_TRACKED(value)) { \
                _PyObject_GC_TRACK(mp); \
                INCREASE_TRACK_COUNT \
            } \
        } \
    } while(0)

void
_PyDict_MaybeUntrack(PyObject *op)
{
    PyDictObject *mp;
    PyObject *value;
    Py_ssize_t mask, i;
    PyDictEntry *ep;

    if (!PyDict_CheckExact(op) || !_PyObject_GC_IS_TRACKED(op))
        return;

    mp = (PyDictObject *) op;
    ep = mp->ma_table;
    mask = mp->ma_mask;
    for (i = 0; i <= mask; i++) {
        if ((value = ep[i].me_value) == NULL)
            continue;
        if (_PyObject_GC_MAY_BE_TRACKED(value) ||
            _PyObject_GC_MAY_BE_TRACKED(ep[i].me_key))
            return;
    }
    DECREASE_TRACK_COUNT
    _PyObject_GC_UNTRACK(op);
}


/*
Internal routine to insert a new item into the table.
Used both by the internal resize routine and by the public insert routine.
Eats a reference to key and one to value.
Returns -1 if an error occurred, or 0 on success.
*/
static int
insertdict(register PyDictObject *mp, PyObject *key, long hash, PyObject *value)
{
    PyObject *old_value;
    register PyDictEntry *ep;
    typedef PyDictEntry *(*lookupfunc)(PyDictObject *, PyObject *, long);

    assert(mp->ma_lookup != NULL);
    ep = mp->ma_lookup(mp, key, hash);
    if (ep == NULL) {
        Py_DECREF(key);
        Py_DECREF(value);
        return -1;
    }
    MAINTAIN_TRACKING(mp, key, value);
    if (ep->me_value != NULL) {
        old_value = ep->me_value;
        ep->me_value = value;
        Py_DECREF(old_value); /* which **CAN** re-enter */
        Py_DECREF(key);
    }
    else {
        if (ep->me_key == NULL)
            mp->ma_fill++;
        else {
            assert(ep->me_key == dummy);
            Py_DECREF(dummy);
        }
        ep->me_key = key;
        ep->me_hash = (Py_ssize_t)hash;
        ep->me_value = value;
        mp->ma_used++;
    }
    return 0;
}

/*
Internal routine used by dictresize() to insert an item which is
known to be absent from the dict.  This routine also assumes that
the dict contains no deleted entries.  Besides the performance benefit,
using insertdict() in dictresize() is dangerous (SF bug #1456209).
Note that no refcounts are changed by this routine; if needed, the caller
is responsible for incref'ing `key` and `value`.
*/
static void
insertdict_clean(register PyDictObject *mp, PyObject *key, long hash,
                 PyObject *value)
{
    register size_t i;
    register size_t perturb;
    register size_t mask = (size_t)mp->ma_mask;
    PyDictEntry *ep0 = mp->ma_table;
    register PyDictEntry *ep;

    MAINTAIN_TRACKING(mp, key, value);
    i = hash & mask;
    ep = &ep0[i];
    for (perturb = hash; ep->me_key != NULL; perturb >>= PERTURB_SHIFT) {
        i = (i << 2) + i + perturb + 1;
        ep = &ep0[i & mask];
    }
    assert(ep->me_value == NULL);
    mp->ma_fill++;
    ep->me_key = key;
    ep->me_hash = (Py_ssize_t)hash;
    ep->me_value = value;
    mp->ma_used++;
}

/*
Restructure the table by allocating a new table and reinserting all
items again.  When entries have been deleted, the new table may
actually be smaller than the old one.
*/
static int
dictresize(PyDictObject *mp, Py_ssize_t minused)
{
    Py_ssize_t newsize;
    PyDictEntry *oldtable, *newtable, *ep;
    Py_ssize_t i;
    int is_oldtable_malloced;
    PyDictEntry small_copy[PyDict_MINSIZE];

    assert(minused >= 0);

    /* Find the smallest table size > minused. */
    for (newsize = PyDict_MINSIZE;
         newsize <= minused && newsize > 0;
         newsize <<= 1)
        ;
    if (newsize <= 0) {
        PyErr_NoMemory();
        return -1;
    }

    /* Get space for a new table. */
    oldtable = mp->ma_table;
    assert(oldtable != NULL);
    is_oldtable_malloced = oldtable != mp->ma_smalltable;

    if (newsize == PyDict_MINSIZE) {
        /* A large table is shrinking, or we can't get any smaller. */
        newtable = mp->ma_smalltable;
        if (newtable == oldtable) {
            if (mp->ma_fill == mp->ma_used) {
                /* No dummies, so no point doing anything. */
                return 0;
            }
            /* We're not going to resize it, but rebuild the
               table anyway to purge old dummy entries.
               Subtle:  This is *necessary* if fill==size,
               as lookdict needs at least one virgin slot to
               terminate failing searches.  If fill < size, it's
               merely desirable, as dummies slow searches. */
            assert(mp->ma_fill > mp->ma_used);
            memcpy(small_copy, oldtable, sizeof(small_copy));
            oldtable = small_copy;
        }
    }
    else {
        newtable = PyMem_NEW(PyDictEntry, newsize);
        if (newtable == NULL) {
            PyErr_NoMemory();
            return -1;
        }
    }

    /* Make the dict empty, using the new table. */
    assert(newtable != oldtable);
    mp->ma_table = newtable;
    mp->ma_mask = newsize - 1;
    memset(newtable, 0, sizeof(PyDictEntry) * newsize);
    mp->ma_used = 0;
    i = mp->ma_fill;
    mp->ma_fill = 0;

    /* Copy the data over; this is refcount-neutral for active entries;
       dummy entries aren't copied over, of course */
    for (ep = oldtable; i > 0; ep++) {
        if (ep->me_value != NULL) {             /* active entry */
            --i;
            insertdict_clean(mp, ep->me_key, (long)ep->me_hash,
                             ep->me_value);
        }
        else if (ep->me_key != NULL) {          /* dummy entry */
            --i;
            assert(ep->me_key == dummy);
            Py_DECREF(ep->me_key);
        }
        /* else key == value == NULL:  nothing to do */
    }

    if (is_oldtable_malloced)
        PyMem_DEL(oldtable);
    return 0;
}

/* Create a new dictionary pre-sized to hold an estimated number of elements.
   Underestimates are okay because the dictionary will resize as necessary.
   Overestimates just mean the dictionary will be more sparse than usual.
*/

PyObject *
_PyDict_NewPresized(Py_ssize_t minused)
{
    PyObject *op = PyDict_New();

    if (minused>5 && op != NULL && dictresize((PyDictObject *)op, minused) == -1) {
        Py_DECREF(op);
        return NULL;
    }
    return op;
}

/* Note that, for historical reasons, PyDict_GetItem() suppresses all errors
 * that may occur (originally dicts supported only string keys, and exceptions
 * weren't possible).  So, while the original intent was that a NULL return
 * meant the key wasn't present, in reality it can mean that, or that an error
 * (suppressed) occurred while computing the key's hash, or that some error
 * (suppressed) occurred when comparing keys in the dict's internal probe
 * sequence.  A nasty example of the latter is when a Python-coded comparison
 * function hits a stack-depth error, which can cause this to return NULL
 * even if the key is present.
 */
PyObject *
PyDict_GetItem(PyObject *op, PyObject *key)
{
    long hash;
    PyDictObject *mp = (PyDictObject *)op;
    PyDictEntry *ep;
    PyThreadState *tstate;
    if (!PyDict_Check(op))
        return NULL;
    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1)
    {
        hash = PyObject_Hash(key);
        if (hash == -1) {
            PyErr_Clear();
            return NULL;
        }
    }

    /* We can arrive here with a NULL tstate during initialization: try
       running "python -Wi" for an example related to string interning.
       Let's just hope that no exception occurs then...  This must be
       _PyThreadState_Current and not PyThreadState_GET() because in debug
       mode, the latter complains if tstate is NULL. */
    tstate = (PyThreadState*)_Py_atomic_load_relaxed(
        &_PyThreadState_Current);
    if (tstate != NULL && tstate->curexc_type != NULL) {
        /* preserve the existing exception */
        PyObject *err_type, *err_value, *err_tb;
        PyErr_Fetch(&err_type, &err_value, &err_tb);
        ep = (mp->ma_lookup)(mp, key, hash);
        /* ignore errors */
        PyErr_Restore(err_type, err_value, err_tb);
        if (ep == NULL)
            return NULL;
    }
    else {
        ep = (mp->ma_lookup)(mp, key, hash);
        if (ep == NULL) {
            PyErr_Clear();
            return NULL;
        }
    }
    return ep->me_value;
}

/* Variant of PyDict_GetItem() that doesn't suppress exceptions.
   This returns NULL *with* an exception set if an exception occurred.
   It returns NULL *without* an exception set if the key wasn't present.
*/
PyObject *
PyDict_GetItemWithError(PyObject *op, PyObject *key)
{
    long hash;
    PyDictObject*mp = (PyDictObject *)op;
    PyDictEntry *ep;

    if (!PyDict_Check(op)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1)
    {
        hash = PyObject_Hash(key);
        if (hash == -1) {
            return NULL;
        }
    }

    ep = (mp->ma_lookup)(mp, key, hash);
    if (ep == NULL)
        return NULL;
    return ep->me_value;
}

/* CAUTION: PyDict_SetItem() must guarantee that it won't resize the
 * dictionary if it's merely replacing the value for an existing key.
 * This means that it's safe to loop over a dictionary with PyDict_Next()
 * and occasionally replace a value -- but you can't insert new keys or
 * remove them.
 */
int
PyDict_SetItem(register PyObject *op, PyObject *key, PyObject *value)
{
    register PyDictObject *mp;
    register long hash;
    register Py_ssize_t n_used;

    if (!PyDict_Check(op)) {
        PyErr_BadInternalCall();
        return -1;
    }
    assert(key);
    assert(value);
    mp = (PyDictObject *)op;
    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1)
    {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return -1;
    }
    assert(mp->ma_fill <= mp->ma_mask);  /* at least one empty slot */
    n_used = mp->ma_used;
    Py_INCREF(value);
    Py_INCREF(key);
    if (insertdict(mp, key, hash, value) != 0)
        return -1;
    /* If we added a key, we can safely resize.  Otherwise just return!
     * If fill >= 2/3 size, adjust size.  Normally, this doubles or
     * quaduples the size, but it's also possible for the dict to shrink
     * (if ma_fill is much larger than ma_used, meaning a lot of dict
     * keys have been * deleted).
     *
     * Quadrupling the size improves average dictionary sparseness
     * (reducing collisions) at the cost of some memory and iteration
     * speed (which loops over every possible entry).  It also halves
     * the number of expensive resize operations in a growing dictionary.
     *
     * Very large dictionaries (over 50K items) use doubling instead.
     * This may help applications with severe memory constraints.
     */
    if (!(mp->ma_used > n_used && mp->ma_fill*3 >= (mp->ma_mask+1)*2))
        return 0;
    return dictresize(mp, (mp->ma_used > 50000 ? 2 : 4) * mp->ma_used);
}

int
PyDict_DelItem(PyObject *op, PyObject *key)
{
    register PyDictObject *mp;
    register long hash;
    register PyDictEntry *ep;
    PyObject *old_value, *old_key;

    if (!PyDict_Check(op)) {
        PyErr_BadInternalCall();
        return -1;
    }
    assert(key);
    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1) {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return -1;
    }
    mp = (PyDictObject *)op;
    ep = (mp->ma_lookup)(mp, key, hash);
    if (ep == NULL)
        return -1;
    if (ep->me_value == NULL) {
        set_key_error(key);
        return -1;
    }
    old_key = ep->me_key;
    Py_INCREF(dummy);
    ep->me_key = dummy;
    old_value = ep->me_value;
    ep->me_value = NULL;
    mp->ma_used--;
    Py_DECREF(old_value);
    Py_DECREF(old_key);
    return 0;
}

void
PyDict_Clear(PyObject *op)
{
    PyDictObject *mp;
    PyDictEntry *ep, *table;
    int table_is_malloced;
    Py_ssize_t fill;
    PyDictEntry small_copy[PyDict_MINSIZE];
#ifdef Py_DEBUG
    Py_ssize_t i, n;
#endif

    if (!PyDict_Check(op))
        return;
    mp = (PyDictObject *)op;
#ifdef Py_DEBUG
    n = mp->ma_mask + 1;
    i = 0;
#endif

    table = mp->ma_table;
    assert(table != NULL);
    table_is_malloced = table != mp->ma_smalltable;

    /* This is delicate.  During the process of clearing the dict,
     * decrefs can cause the dict to mutate.  To avoid fatal confusion
     * (voice of experience), we have to make the dict empty before
     * clearing the slots, and never refer to anything via mp->xxx while
     * clearing.
     */
    fill = mp->ma_fill;
    if (table_is_malloced)
        EMPTY_TO_MINSIZE(mp);

    else if (fill > 0) {
        /* It's a small table with something that needs to be cleared.
         * Afraid the only safe way is to copy the dict entries into
         * another small table first.
         */
        memcpy(small_copy, table, sizeof(small_copy));
        table = small_copy;
        EMPTY_TO_MINSIZE(mp);
    }
    /* else it's a small table that's already empty */

    /* Now we can finally clear things.  If C had refcounts, we could
     * assert that the refcount on table is 1 now, i.e. that this function
     * has unique access to it, so decref side-effects can't alter it.
     */
    for (ep = table; fill > 0; ++ep) {
#ifdef Py_DEBUG
        assert(i < n);
        ++i;
#endif
        if (ep->me_key) {
            --fill;
            Py_DECREF(ep->me_key);
            Py_XDECREF(ep->me_value);
        }
#ifdef Py_DEBUG
        else
            assert(ep->me_value == NULL);
#endif
    }

    if (table_is_malloced)
        PyMem_DEL(table);
}

/*
 * Iterate over a dict.  Use like so:
 *
 *     Py_ssize_t i;
 *     PyObject *key, *value;
 *     i = 0;   # important!  i should not otherwise be changed by you
 *     while (PyDict_Next(yourdict, &i, &key, &value)) {
 *              Refer to borrowed references in key and value.
 *     }
 *
 * CAUTION:  In general, it isn't safe to use PyDict_Next in a loop that
 * mutates the dict.  One exception:  it is safe if the loop merely changes
 * the values associated with the keys (but doesn't insert new keys or
 * delete keys), via PyDict_SetItem().
 */
int
PyDict_Next(PyObject *op, Py_ssize_t *ppos, PyObject **pkey, PyObject **pvalue)
{
    register Py_ssize_t i;
    register Py_ssize_t mask;
    register PyDictEntry *ep;

    if (!PyDict_Check(op))
        return 0;
    i = *ppos;
    if (i < 0)
        return 0;
    ep = ((PyDictObject *)op)->ma_table;
    mask = ((PyDictObject *)op)->ma_mask;
    while (i <= mask && ep[i].me_value == NULL)
        i++;
    *ppos = i+1;
    if (i > mask)
        return 0;
    if (pkey)
        *pkey = ep[i].me_key;
    if (pvalue)
        *pvalue = ep[i].me_value;
    return 1;
}

/* Internal version of PyDict_Next that returns a hash value in addition to the key and value.*/
int
_PyDict_Next(PyObject *op, Py_ssize_t *ppos, PyObject **pkey, PyObject **pvalue, long *phash)
{
    register Py_ssize_t i;
    register Py_ssize_t mask;
    register PyDictEntry *ep;

    if (!PyDict_Check(op))
        return 0;
    i = *ppos;
    if (i < 0)
        return 0;
    ep = ((PyDictObject *)op)->ma_table;
    mask = ((PyDictObject *)op)->ma_mask;
    while (i <= mask && ep[i].me_value == NULL)
        i++;
    *ppos = i+1;
    if (i > mask)
        return 0;
    *phash = (long)(ep[i].me_hash);
    if (pkey)
        *pkey = ep[i].me_key;
    if (pvalue)
        *pvalue = ep[i].me_value;
    return 1;
}

/* Methods */

static void
dict_dealloc(register PyDictObject *mp)
{
    register PyDictEntry *ep;
    Py_ssize_t fill = mp->ma_fill;
    PyObject_GC_UnTrack(mp);
    Py_TRASHCAN_SAFE_BEGIN(mp)
    for (ep = mp->ma_table; fill > 0; ep++) {
        if (ep->me_key) {
            --fill;
            Py_DECREF(ep->me_key);
            Py_XDECREF(ep->me_value);
        }
    }
    if (mp->ma_table != mp->ma_smalltable)
        PyMem_DEL(mp->ma_table);
    if (numfree < PyDict_MAXFREELIST && Py_TYPE(mp) == &PyDict_Type)
        free_list[numfree++] = mp;
    else
        Py_TYPE(mp)->tp_free((PyObject *)mp);
    Py_TRASHCAN_SAFE_END(mp)
}

static PyObject *
dict_repr(PyDictObject *mp)
{
    Py_ssize_t i;
    PyObject *s, *temp, *colon = NULL;
    PyObject *pieces = NULL, *result = NULL;
    PyObject *key, *value;

    i = Py_ReprEnter((PyObject *)mp);
    if (i != 0) {
        return i > 0 ? PyUnicode_FromString("{...}") : NULL;
    }

    if (mp->ma_used == 0) {
        result = PyUnicode_FromString("{}");
        goto Done;
    }

    pieces = PyList_New(0);
    if (pieces == NULL)
        goto Done;

    colon = PyUnicode_FromString(": ");
    if (colon == NULL)
        goto Done;

    /* Do repr() on each key+value pair, and insert ": " between them.
       Note that repr may mutate the dict. */
    i = 0;
    while (PyDict_Next((PyObject *)mp, &i, &key, &value)) {
        int status;
        /* Prevent repr from deleting value during key format. */
        Py_INCREF(value);
        s = PyObject_Repr(key);
        PyUnicode_Append(&s, colon);
        PyUnicode_AppendAndDel(&s, PyObject_Repr(value));
        Py_DECREF(value);
        if (s == NULL)
            goto Done;
        status = PyList_Append(pieces, s);
        Py_DECREF(s);  /* append created a new ref */
        if (status < 0)
            goto Done;
    }

    /* Add "{}" decorations to the first and last items. */
    assert(PyList_GET_SIZE(pieces) > 0);
    s = PyUnicode_FromString("{");
    if (s == NULL)
        goto Done;
    temp = PyList_GET_ITEM(pieces, 0);
    PyUnicode_AppendAndDel(&s, temp);
    PyList_SET_ITEM(pieces, 0, s);
    if (s == NULL)
        goto Done;

    s = PyUnicode_FromString("}");
    if (s == NULL)
        goto Done;
    temp = PyList_GET_ITEM(pieces, PyList_GET_SIZE(pieces) - 1);
    PyUnicode_AppendAndDel(&temp, s);
    PyList_SET_ITEM(pieces, PyList_GET_SIZE(pieces) - 1, temp);
    if (temp == NULL)
        goto Done;

    /* Paste them all together with ", " between. */
    s = PyUnicode_FromString(", ");
    if (s == NULL)
        goto Done;
    result = PyUnicode_Join(s, pieces);
    Py_DECREF(s);

Done:
    Py_XDECREF(pieces);
    Py_XDECREF(colon);
    Py_ReprLeave((PyObject *)mp);
    return result;
}

static Py_ssize_t
dict_length(PyDictObject *mp)
{
    return mp->ma_used;
}

static PyObject *
dict_subscript(PyDictObject *mp, register PyObject *key)
{
    PyObject *v;
    long hash;
    PyDictEntry *ep;
    assert(mp->ma_table != NULL);
    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1) {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return NULL;
    }
    ep = (mp->ma_lookup)(mp, key, hash);
    if (ep == NULL)
        return NULL;
    v = ep->me_value;
    if (v == NULL) {
        if (!PyDict_CheckExact(mp)) {
            /* Look up __missing__ method if we're a subclass. */
            PyObject *missing, *res;
            static PyObject *missing_str = NULL;
            missing = _PyObject_LookupSpecial((PyObject *)mp,
                                              "__missing__",
                                              &missing_str);
            if (missing != NULL) {
                res = PyObject_CallFunctionObjArgs(missing,
                                                   key, NULL);
                Py_DECREF(missing);
                return res;
            }
            else if (PyErr_Occurred())
                return NULL;
        }
        set_key_error(key);
        return NULL;
    }
    else
        Py_INCREF(v);
    return v;
}

static int
dict_ass_sub(PyDictObject *mp, PyObject *v, PyObject *w)
{
    if (w == NULL)
        return PyDict_DelItem((PyObject *)mp, v);
    else
        return PyDict_SetItem((PyObject *)mp, v, w);
}

static PyMappingMethods dict_as_mapping = {
    (lenfunc)dict_length, /*mp_length*/
    (binaryfunc)dict_subscript, /*mp_subscript*/
    (objobjargproc)dict_ass_sub, /*mp_ass_subscript*/
};

static PyObject *
dict_keys(register PyDictObject *mp)
{
    register PyObject *v;
    register Py_ssize_t i, j;
    PyDictEntry *ep;
    Py_ssize_t mask, n;

  again:
    n = mp->ma_used;
    v = PyList_New(n);
    if (v == NULL)
        return NULL;
    if (n != mp->ma_used) {
        /* Durnit.  The allocations caused the dict to resize.
         * Just start over, this shouldn't normally happen.
         */
        Py_DECREF(v);
        goto again;
    }
    ep = mp->ma_table;
    mask = mp->ma_mask;
    for (i = 0, j = 0; i <= mask; i++) {
        if (ep[i].me_value != NULL) {
            PyObject *key = ep[i].me_key;
            Py_INCREF(key);
            PyList_SET_ITEM(v, j, key);
            j++;
        }
    }
    assert(j == n);
    return v;
}

static PyObject *
dict_values(register PyDictObject *mp)
{
    register PyObject *v;
    register Py_ssize_t i, j;
    PyDictEntry *ep;
    Py_ssize_t mask, n;

  again:
    n = mp->ma_used;
    v = PyList_New(n);
    if (v == NULL)
        return NULL;
    if (n != mp->ma_used) {
        /* Durnit.  The allocations caused the dict to resize.
         * Just start over, this shouldn't normally happen.
         */
        Py_DECREF(v);
        goto again;
    }
    ep = mp->ma_table;
    mask = mp->ma_mask;
    for (i = 0, j = 0; i <= mask; i++) {
        if (ep[i].me_value != NULL) {
            PyObject *value = ep[i].me_value;
            Py_INCREF(value);
            PyList_SET_ITEM(v, j, value);
            j++;
        }
    }
    assert(j == n);
    return v;
}

static PyObject *
dict_items(register PyDictObject *mp)
{
    register PyObject *v;
    register Py_ssize_t i, j, n;
    Py_ssize_t mask;
    PyObject *item, *key, *value;
    PyDictEntry *ep;

    /* Preallocate the list of tuples, to avoid allocations during
     * the loop over the items, which could trigger GC, which
     * could resize the dict. :-(
     */
  again:
    n = mp->ma_used;
    v = PyList_New(n);
    if (v == NULL)
        return NULL;
    for (i = 0; i < n; i++) {
        item = PyTuple_New(2);
        if (item == NULL) {
            Py_DECREF(v);
            return NULL;
        }
        PyList_SET_ITEM(v, i, item);
    }
    if (n != mp->ma_used) {
        /* Durnit.  The allocations caused the dict to resize.
         * Just start over, this shouldn't normally happen.
         */
        Py_DECREF(v);
        goto again;
    }
    /* Nothing we do below makes any function calls. */
    ep = mp->ma_table;
    mask = mp->ma_mask;
    for (i = 0, j = 0; i <= mask; i++) {
        if ((value=ep[i].me_value) != NULL) {
            key = ep[i].me_key;
            item = PyList_GET_ITEM(v, j);
            Py_INCREF(key);
            PyTuple_SET_ITEM(item, 0, key);
            Py_INCREF(value);
            PyTuple_SET_ITEM(item, 1, value);
            j++;
        }
    }
    assert(j == n);
    return v;
}

static PyObject *
dict_fromkeys(PyObject *cls, PyObject *args)
{
    PyObject *seq;
    PyObject *value = Py_None;
    PyObject *it;       /* iter(seq) */
    PyObject *key;
    PyObject *d;
    int status;

    if (!PyArg_UnpackTuple(args, "fromkeys", 1, 2, &seq, &value))
        return NULL;

    d = PyObject_CallObject(cls, NULL);
    if (d == NULL)
        return NULL;

    if (PyDict_CheckExact(d) && PyDict_CheckExact(seq)) {
        PyDictObject *mp = (PyDictObject *)d;
        PyObject *oldvalue;
        Py_ssize_t pos = 0;
        PyObject *key;
        long hash;

        if (dictresize(mp, Py_SIZE(seq)))
            return NULL;

        while (_PyDict_Next(seq, &pos, &key, &oldvalue, &hash)) {
            Py_INCREF(key);
            Py_INCREF(value);
            if (insertdict(mp, key, hash, value))
                return NULL;
        }
        return d;
    }

    if (PyDict_CheckExact(d) && PyAnySet_CheckExact(seq)) {
        PyDictObject *mp = (PyDictObject *)d;
        Py_ssize_t pos = 0;
        PyObject *key;
        long hash;

        if (dictresize(mp, PySet_GET_SIZE(seq)))
            return NULL;

        while (_PySet_NextEntry(seq, &pos, &key, &hash)) {
            Py_INCREF(key);
            Py_INCREF(value);
            if (insertdict(mp, key, hash, value))
                return NULL;
        }
        return d;
    }

    it = PyObject_GetIter(seq);
    if (it == NULL){
        Py_DECREF(d);
        return NULL;
    }

    if (PyDict_CheckExact(d)) {
        while ((key = PyIter_Next(it)) != NULL) {
            status = PyDict_SetItem(d, key, value);
            Py_DECREF(key);
            if (status < 0)
                goto Fail;
        }
    } else {
        while ((key = PyIter_Next(it)) != NULL) {
            status = PyObject_SetItem(d, key, value);
            Py_DECREF(key);
            if (status < 0)
                goto Fail;
        }
    }

    if (PyErr_Occurred())
        goto Fail;
    Py_DECREF(it);
    return d;

Fail:
    Py_DECREF(it);
    Py_DECREF(d);
    return NULL;
}

static int
dict_update_common(PyObject *self, PyObject *args, PyObject *kwds, char *methname)
{
    PyObject *arg = NULL;
    int result = 0;

    if (!PyArg_UnpackTuple(args, methname, 0, 1, &arg))
        result = -1;

    else if (arg != NULL) {
        if (PyObject_HasAttrString(arg, "keys"))
            result = PyDict_Merge(self, arg, 1);
        else
            result = PyDict_MergeFromSeq2(self, arg, 1);
    }
    if (result == 0 && kwds != NULL) {
        if (PyArg_ValidateKeywordArguments(kwds))
            result = PyDict_Merge(self, kwds, 1);
        else
            result = -1;
    }
    return result;
}

static PyObject *
dict_update(PyObject *self, PyObject *args, PyObject *kwds)
{
    if (dict_update_common(self, args, kwds, "update") != -1)
        Py_RETURN_NONE;
    return NULL;
}

/* Update unconditionally replaces existing items.
   Merge has a 3rd argument 'override'; if set, it acts like Update,
   otherwise it leaves existing items unchanged.

   PyDict_{Update,Merge} update/merge from a mapping object.

   PyDict_MergeFromSeq2 updates/merges from any iterable object
   producing iterable objects of length 2.
*/

int
PyDict_MergeFromSeq2(PyObject *d, PyObject *seq2, int override)
{
    PyObject *it;       /* iter(seq2) */
    Py_ssize_t i;       /* index into seq2 of current element */
    PyObject *item;     /* seq2[i] */
    PyObject *fast;     /* item as a 2-tuple or 2-list */

    assert(d != NULL);
    assert(PyDict_Check(d));
    assert(seq2 != NULL);

    it = PyObject_GetIter(seq2);
    if (it == NULL)
        return -1;

    for (i = 0; ; ++i) {
        PyObject *key, *value;
        Py_ssize_t n;

        fast = NULL;
        item = PyIter_Next(it);
        if (item == NULL) {
            if (PyErr_Occurred())
                goto Fail;
            break;
        }

        /* Convert item to sequence, and verify length 2. */
        fast = PySequence_Fast(item, "");
        if (fast == NULL) {
            if (PyErr_ExceptionMatches(PyExc_TypeError))
                PyErr_Format(PyExc_TypeError,
                    "cannot convert dictionary update "
                    "sequence element #%zd to a sequence",
                    i);
            goto Fail;
        }
        n = PySequence_Fast_GET_SIZE(fast);
        if (n != 2) {
            PyErr_Format(PyExc_ValueError,
                         "dictionary update sequence element #%zd "
                         "has length %zd; 2 is required",
                         i, n);
            goto Fail;
        }

        /* Update/merge with this (key, value) pair. */
        key = PySequence_Fast_GET_ITEM(fast, 0);
        value = PySequence_Fast_GET_ITEM(fast, 1);
        if (override || PyDict_GetItem(d, key) == NULL) {
            int status = PyDict_SetItem(d, key, value);
            if (status < 0)
                goto Fail;
        }
        Py_DECREF(fast);
        Py_DECREF(item);
    }

    i = 0;
    goto Return;
Fail:
    Py_XDECREF(item);
    Py_XDECREF(fast);
    i = -1;
Return:
    Py_DECREF(it);
    return Py_SAFE_DOWNCAST(i, Py_ssize_t, int);
}

int
PyDict_Update(PyObject *a, PyObject *b)
{
    return PyDict_Merge(a, b, 1);
}

int
PyDict_Merge(PyObject *a, PyObject *b, int override)
{
    register PyDictObject *mp, *other;
    register Py_ssize_t i;
    PyDictEntry *entry;

    /* We accept for the argument either a concrete dictionary object,
     * or an abstract "mapping" object.  For the former, we can do
     * things quite efficiently.  For the latter, we only require that
     * PyMapping_Keys() and PyObject_GetItem() be supported.
     */
    if (a == NULL || !PyDict_Check(a) || b == NULL) {
        PyErr_BadInternalCall();
        return -1;
    }
    mp = (PyDictObject*)a;
    if (PyDict_Check(b)) {
        other = (PyDictObject*)b;
        if (other == mp || other->ma_used == 0)
            /* a.update(a) or a.update({}); nothing to do */
            return 0;
        if (mp->ma_used == 0)
            /* Since the target dict is empty, PyDict_GetItem()
             * always returns NULL.  Setting override to 1
             * skips the unnecessary test.
             */
            override = 1;
        /* Do one big resize at the start, rather than
         * incrementally resizing as we insert new items.  Expect
         * that there will be no (or few) overlapping keys.
         */
        if ((mp->ma_fill + other->ma_used)*3 >= (mp->ma_mask+1)*2) {
           if (dictresize(mp, (mp->ma_used + other->ma_used)*2) != 0)
               return -1;
        }
        for (i = 0; i <= other->ma_mask; i++) {
            entry = &other->ma_table[i];
            if (entry->me_value != NULL &&
                (override ||
                 PyDict_GetItem(a, entry->me_key) == NULL)) {
                Py_INCREF(entry->me_key);
                Py_INCREF(entry->me_value);
                if (insertdict(mp, entry->me_key,
                               (long)entry->me_hash,
                               entry->me_value) != 0)
                    return -1;
            }
        }
    }
    else {
        /* Do it the generic, slower way */
        PyObject *keys = PyMapping_Keys(b);
        PyObject *iter;
        PyObject *key, *value;
        int status;

        if (keys == NULL)
            /* Docstring says this is equivalent to E.keys() so
             * if E doesn't have a .keys() method we want
             * AttributeError to percolate up.  Might as well
             * do the same for any other error.
             */
            return -1;

        iter = PyObject_GetIter(keys);
        Py_DECREF(keys);
        if (iter == NULL)
            return -1;

        for (key = PyIter_Next(iter); key; key = PyIter_Next(iter)) {
            if (!override && PyDict_GetItem(a, key) != NULL) {
                Py_DECREF(key);
                continue;
            }
            value = PyObject_GetItem(b, key);
            if (value == NULL) {
                Py_DECREF(iter);
                Py_DECREF(key);
                return -1;
            }
            status = PyDict_SetItem(a, key, value);
            Py_DECREF(key);
            Py_DECREF(value);
            if (status < 0) {
                Py_DECREF(iter);
                return -1;
            }
        }
        Py_DECREF(iter);
        if (PyErr_Occurred())
            /* Iterator completed, via error */
            return -1;
    }
    return 0;
}

static PyObject *
dict_copy(register PyDictObject *mp)
{
    return PyDict_Copy((PyObject*)mp);
}

PyObject *
PyDict_Copy(PyObject *o)
{
    PyObject *copy;

    if (o == NULL || !PyDict_Check(o)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    copy = PyDict_New();
    if (copy == NULL)
        return NULL;
    if (PyDict_Merge(copy, o, 1) == 0)
        return copy;
    Py_DECREF(copy);
    return NULL;
}

Py_ssize_t
PyDict_Size(PyObject *mp)
{
    if (mp == NULL || !PyDict_Check(mp)) {
        PyErr_BadInternalCall();
        return -1;
    }
    return ((PyDictObject *)mp)->ma_used;
}

PyObject *
PyDict_Keys(PyObject *mp)
{
    if (mp == NULL || !PyDict_Check(mp)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    return dict_keys((PyDictObject *)mp);
}

PyObject *
PyDict_Values(PyObject *mp)
{
    if (mp == NULL || !PyDict_Check(mp)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    return dict_values((PyDictObject *)mp);
}

PyObject *
PyDict_Items(PyObject *mp)
{
    if (mp == NULL || !PyDict_Check(mp)) {
        PyErr_BadInternalCall();
        return NULL;
    }
    return dict_items((PyDictObject *)mp);
}

/* Return 1 if dicts equal, 0 if not, -1 if error.
 * Gets out as soon as any difference is detected.
 * Uses only Py_EQ comparison.
 */
static int
dict_equal(PyDictObject *a, PyDictObject *b)
{
    Py_ssize_t i;

    if (a->ma_used != b->ma_used)
        /* can't be equal if # of entries differ */
        return 0;

    /* Same # of entries -- check all of 'em.  Exit early on any diff. */
    for (i = 0; i <= a->ma_mask; i++) {
        PyObject *aval = a->ma_table[i].me_value;
        if (aval != NULL) {
            int cmp;
            PyObject *bval;
            PyObject *key = a->ma_table[i].me_key;
            /* temporarily bump aval's refcount to ensure it stays
               alive until we're done with it */
            Py_INCREF(aval);
            /* ditto for key */
            Py_INCREF(key);
            bval = PyDict_GetItemWithError((PyObject *)b, key);
            Py_DECREF(key);
            if (bval == NULL) {
                Py_DECREF(aval);
                if (PyErr_Occurred())
                    return -1;
                return 0;
            }
            cmp = PyObject_RichCompareBool(aval, bval, Py_EQ);
            Py_DECREF(aval);
            if (cmp <= 0)  /* error or not equal */
                return cmp;
        }
    }
    return 1;
 }

static PyObject *
dict_richcompare(PyObject *v, PyObject *w, int op)
{
    int cmp;
    PyObject *res;

    if (!PyDict_Check(v) || !PyDict_Check(w)) {
        res = Py_NotImplemented;
    }
    else if (op == Py_EQ || op == Py_NE) {
        cmp = dict_equal((PyDictObject *)v, (PyDictObject *)w);
        if (cmp < 0)
            return NULL;
        res = (cmp == (op == Py_EQ)) ? Py_True : Py_False;
    }
    else
        res = Py_NotImplemented;
    Py_INCREF(res);
    return res;
 }

static PyObject *
dict_contains(register PyDictObject *mp, PyObject *key)
{
    long hash;
    PyDictEntry *ep;

    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1) {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return NULL;
    }
    ep = (mp->ma_lookup)(mp, key, hash);
    if (ep == NULL)
        return NULL;
    return PyBool_FromLong(ep->me_value != NULL);
}

static PyObject *
dict_get(register PyDictObject *mp, PyObject *args)
{
    PyObject *key;
    PyObject *failobj = Py_None;
    PyObject *val = NULL;
    long hash;
    PyDictEntry *ep;

    if (!PyArg_UnpackTuple(args, "get", 1, 2, &key, &failobj))
        return NULL;

    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1) {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return NULL;
    }
    ep = (mp->ma_lookup)(mp, key, hash);
    if (ep == NULL)
        return NULL;
    val = ep->me_value;
    if (val == NULL)
        val = failobj;
    Py_INCREF(val);
    return val;
}


static PyObject *
dict_setdefault(register PyDictObject *mp, PyObject *args)
{
    PyObject *key;
    PyObject *failobj = Py_None;
    PyObject *val = NULL;
    long hash;
    PyDictEntry *ep;

    if (!PyArg_UnpackTuple(args, "setdefault", 1, 2, &key, &failobj))
        return NULL;

    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1) {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return NULL;
    }
    ep = (mp->ma_lookup)(mp, key, hash);
    if (ep == NULL)
        return NULL;
    val = ep->me_value;
    if (val == NULL) {
        val = failobj;
        if (PyDict_SetItem((PyObject*)mp, key, failobj))
            val = NULL;
    }
    Py_XINCREF(val);
    return val;
}


static PyObject *
dict_clear(register PyDictObject *mp)
{
    PyDict_Clear((PyObject *)mp);
    Py_RETURN_NONE;
}

static PyObject *
dict_pop(PyDictObject *mp, PyObject *args)
{
    long hash;
    PyDictEntry *ep;
    PyObject *old_value, *old_key;
    PyObject *key, *deflt = NULL;

    if(!PyArg_UnpackTuple(args, "pop", 1, 2, &key, &deflt))
        return NULL;
    if (mp->ma_used == 0) {
        if (deflt) {
            Py_INCREF(deflt);
            return deflt;
        }
        PyErr_SetString(PyExc_KeyError,
                        "pop(): dictionary is empty");
        return NULL;
    }
    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1) {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return NULL;
    }
    ep = (mp->ma_lookup)(mp, key, hash);
    if (ep == NULL)
        return NULL;
    if (ep->me_value == NULL) {
        if (deflt) {
            Py_INCREF(deflt);
            return deflt;
        }
        set_key_error(key);
        return NULL;
    }
    old_key = ep->me_key;
    Py_INCREF(dummy);
    ep->me_key = dummy;
    old_value = ep->me_value;
    ep->me_value = NULL;
    mp->ma_used--;
    Py_DECREF(old_key);
    return old_value;
}

static PyObject *
dict_popitem(PyDictObject *mp)
{
    Py_ssize_t i = 0;
    PyDictEntry *ep;
    PyObject *res;

    /* Allocate the result tuple before checking the size.  Believe it
     * or not, this allocation could trigger a garbage collection which
     * could empty the dict, so if we checked the size first and that
     * happened, the result would be an infinite loop (searching for an
     * entry that no longer exists).  Note that the usual popitem()
     * idiom is "while d: k, v = d.popitem()". so needing to throw the
     * tuple away if the dict *is* empty isn't a significant
     * inefficiency -- possible, but unlikely in practice.
     */
    res = PyTuple_New(2);
    if (res == NULL)
        return NULL;
    if (mp->ma_used == 0) {
        Py_DECREF(res);
        PyErr_SetString(PyExc_KeyError,
                        "popitem(): dictionary is empty");
        return NULL;
    }
    /* Set ep to "the first" dict entry with a value.  We abuse the hash
     * field of slot 0 to hold a search finger:
     * If slot 0 has a value, use slot 0.
     * Else slot 0 is being used to hold a search finger,
     * and we use its hash value as the first index to look.
     */
    ep = &mp->ma_table[0];
    if (ep->me_value == NULL) {
        i = ep->me_hash;
        /* The hash field may be a real hash value, or it may be a
         * legit search finger, or it may be a once-legit search
         * finger that's out of bounds now because it wrapped around
         * or the table shrunk -- simply make sure it's in bounds now.
         */
        if (i > mp->ma_mask || i < 1)
            i = 1;              /* skip slot 0 */
        while ((ep = &mp->ma_table[i])->me_value == NULL) {
            i++;
            if (i > mp->ma_mask)
                i = 1;
        }
    }
    PyTuple_SET_ITEM(res, 0, ep->me_key);
    PyTuple_SET_ITEM(res, 1, ep->me_value);
    Py_INCREF(dummy);
    ep->me_key = dummy;
    ep->me_value = NULL;
    mp->ma_used--;
    assert(mp->ma_table[0].me_value == NULL);
    mp->ma_table[0].me_hash = i + 1;  /* next place to start */
    return res;
}

static int
dict_traverse(PyObject *op, visitproc visit, void *arg)
{
    Py_ssize_t i = 0;
    PyObject *pk;
    PyObject *pv;

    while (PyDict_Next(op, &i, &pk, &pv)) {
        Py_VISIT(pk);
        Py_VISIT(pv);
    }
    return 0;
}

static int
dict_tp_clear(PyObject *op)
{
    PyDict_Clear(op);
    return 0;
}

static PyObject *dictiter_new(PyDictObject *, PyTypeObject *);

static PyObject *
dict_sizeof(PyDictObject *mp)
{
    Py_ssize_t res;

    res = sizeof(PyDictObject);
    if (mp->ma_table != mp->ma_smalltable)
        res = res + (mp->ma_mask + 1) * sizeof(PyDictEntry);
    return PyLong_FromSsize_t(res);
}

PyDoc_STRVAR(contains__doc__,
"D.__contains__(k) -> True if D has a key k, else False");

PyDoc_STRVAR(getitem__doc__, "x.__getitem__(y) <==> x[y]");

PyDoc_STRVAR(sizeof__doc__,
"D.__sizeof__() -> size of D in memory, in bytes");

PyDoc_STRVAR(get__doc__,
"D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None.");

PyDoc_STRVAR(setdefault_doc__,
"D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D");

PyDoc_STRVAR(pop__doc__,
"D.pop(k[,d]) -> v, remove specified key and return the corresponding value.\n\
If key is not found, d is returned if given, otherwise KeyError is raised");

PyDoc_STRVAR(popitem__doc__,
"D.popitem() -> (k, v), remove and return some (key, value) pair as a\n\
2-tuple; but raise KeyError if D is empty.");

PyDoc_STRVAR(update__doc__,
"D.update(E, **F) -> None.  Update D from dict/iterable E and F.\n"
"If E has a .keys() method, does:     for k in E: D[k] = E[k]\n\
If E lacks .keys() method, does:     for (k, v) in E: D[k] = v\n\
In either case, this is followed by: for k in F: D[k] = F[k]");

PyDoc_STRVAR(fromkeys__doc__,
"dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v.\n\
v defaults to None.");

PyDoc_STRVAR(clear__doc__,
"D.clear() -> None.  Remove all items from D.");

PyDoc_STRVAR(copy__doc__,
"D.copy() -> a shallow copy of D");

/* Forward */
static PyObject *dictkeys_new(PyObject *);
static PyObject *dictitems_new(PyObject *);
static PyObject *dictvalues_new(PyObject *);

PyDoc_STRVAR(keys__doc__,
             "D.keys() -> a set-like object providing a view on D's keys");
PyDoc_STRVAR(items__doc__,
             "D.items() -> a set-like object providing a view on D's items");
PyDoc_STRVAR(values__doc__,
             "D.values() -> an object providing a view on D's values");

static PyMethodDef mapp_methods[] = {
    {"__contains__",(PyCFunction)dict_contains,     METH_O | METH_COEXIST,
     contains__doc__},
    {"__getitem__", (PyCFunction)dict_subscript,        METH_O | METH_COEXIST,
     getitem__doc__},
    {"__sizeof__",      (PyCFunction)dict_sizeof,       METH_NOARGS,
     sizeof__doc__},
    {"get",         (PyCFunction)dict_get,          METH_VARARGS,
     get__doc__},
    {"setdefault",  (PyCFunction)dict_setdefault,   METH_VARARGS,
     setdefault_doc__},
    {"pop",         (PyCFunction)dict_pop,          METH_VARARGS,
     pop__doc__},
    {"popitem",         (PyCFunction)dict_popitem,      METH_NOARGS,
     popitem__doc__},
    {"keys",            (PyCFunction)dictkeys_new,      METH_NOARGS,
    keys__doc__},
    {"items",           (PyCFunction)dictitems_new,     METH_NOARGS,
    items__doc__},
    {"values",          (PyCFunction)dictvalues_new,    METH_NOARGS,
    values__doc__},
    {"update",          (PyCFunction)dict_update,       METH_VARARGS | METH_KEYWORDS,
     update__doc__},
    {"fromkeys",        (PyCFunction)dict_fromkeys,     METH_VARARGS | METH_CLASS,
     fromkeys__doc__},
    {"clear",           (PyCFunction)dict_clear,        METH_NOARGS,
     clear__doc__},
    {"copy",            (PyCFunction)dict_copy,         METH_NOARGS,
     copy__doc__},
    {NULL,              NULL}   /* sentinel */
};

/* Return 1 if `key` is in dict `op`, 0 if not, and -1 on error. */
int
PyDict_Contains(PyObject *op, PyObject *key)
{
    long hash;
    PyDictObject *mp = (PyDictObject *)op;
    PyDictEntry *ep;

    if (!PyUnicode_CheckExact(key) ||
        (hash = ((PyUnicodeObject *) key)->hash) == -1) {
        hash = PyObject_Hash(key);
        if (hash == -1)
            return -1;
    }
    ep = (mp->ma_lookup)(mp, key, hash);
    return ep == NULL ? -1 : (ep->me_value != NULL);
}

/* Internal version of PyDict_Contains used when the hash value is already known */
int
_PyDict_Contains(PyObject *op, PyObject *key, long hash)
{
    PyDictObject *mp = (PyDictObject *)op;
    PyDictEntry *ep;

    ep = (mp->ma_lookup)(mp, key, hash);
    return ep == NULL ? -1 : (ep->me_value != NULL);
}

/* Hack to implement "key in dict" */
static PySequenceMethods dict_as_sequence = {
    0,                          /* sq_length */
    0,                          /* sq_concat */
    0,                          /* sq_repeat */
    0,                          /* sq_item */
    0,                          /* sq_slice */
    0,                          /* sq_ass_item */
    0,                          /* sq_ass_slice */
    PyDict_Contains,            /* sq_contains */
    0,                          /* sq_inplace_concat */
    0,                          /* sq_inplace_repeat */
};

static PyObject *
dict_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    PyObject *self;

    assert(type != NULL && type->tp_alloc != NULL);
    self = type->tp_alloc(type, 0);
    if (self != NULL) {
        PyDictObject *d = (PyDictObject *)self;
        /* It's guaranteed that tp->alloc zeroed out the struct. */
        assert(d->ma_table == NULL && d->ma_fill == 0 && d->ma_used == 0);
        INIT_NONZERO_DICT_SLOTS(d);
        d->ma_lookup = lookdict_unicode;
        /* The object has been implicitely tracked by tp_alloc */
        if (type == &PyDict_Type)
            _PyObject_GC_UNTRACK(d);
#ifdef SHOW_CONVERSION_COUNTS
        ++created;
#endif
#ifdef SHOW_TRACK_COUNT
        if (_PyObject_GC_IS_TRACKED(d))
            count_tracked++;
        else
            count_untracked++;
#endif
    }
    return self;
}

static int
dict_init(PyObject *self, PyObject *args, PyObject *kwds)
{
    return dict_update_common(self, args, kwds, "dict");
}

static PyObject *
dict_iter(PyDictObject *dict)
{
    return dictiter_new(dict, &PyDictIterKey_Type);
}

PyDoc_STRVAR(dictionary_doc,
"dict() -> new empty dictionary\n"
"dict(mapping) -> new dictionary initialized from a mapping object's\n"
"    (key, value) pairs\n"
"dict(iterable) -> new dictionary initialized as if via:\n"
"    d = {}\n"
"    for k, v in iterable:\n"
"        d[k] = v\n"
"dict(**kwargs) -> new dictionary initialized with the name=value pairs\n"
"    in the keyword argument list.  For example:  dict(one=1, two=2)");

PyTypeObject PyDict_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "dict",
    sizeof(PyDictObject),
    0,
    (destructor)dict_dealloc,                   /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    (reprfunc)dict_repr,                        /* tp_repr */
    0,                                          /* tp_as_number */
    &dict_as_sequence,                          /* tp_as_sequence */
    &dict_as_mapping,                           /* tp_as_mapping */
    (hashfunc)PyObject_HashNotImplemented,      /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
        Py_TPFLAGS_BASETYPE | Py_TPFLAGS_DICT_SUBCLASS,         /* tp_flags */
    dictionary_doc,                             /* tp_doc */
    dict_traverse,                              /* tp_traverse */
    dict_tp_clear,                              /* tp_clear */
    dict_richcompare,                           /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    (getiterfunc)dict_iter,                     /* tp_iter */
    0,                                          /* tp_iternext */
    mapp_methods,                               /* tp_methods */
    0,                                          /* tp_members */
    0,                                          /* tp_getset */
    0,                                          /* tp_base */
    0,                                          /* tp_dict */
    0,                                          /* tp_descr_get */
    0,                                          /* tp_descr_set */
    0,                                          /* tp_dictoffset */
    dict_init,                                  /* tp_init */
    PyType_GenericAlloc,                        /* tp_alloc */
    dict_new,                                   /* tp_new */
    PyObject_GC_Del,                            /* tp_free */
};

/* For backward compatibility with old dictionary interface */

PyObject *
PyDict_GetItemString(PyObject *v, const char *key)
{
    PyObject *kv, *rv;
    kv = PyUnicode_FromString(key);
    if (kv == NULL)
        return NULL;
    rv = PyDict_GetItem(v, kv);
    Py_DECREF(kv);
    return rv;
}

int
PyDict_SetItemString(PyObject *v, const char *key, PyObject *item)
{
    PyObject *kv;
    int err;
    kv = PyUnicode_FromString(key);
    if (kv == NULL)
        return -1;
    PyUnicode_InternInPlace(&kv); /* XXX Should we really? */
    err = PyDict_SetItem(v, kv, item);
    Py_DECREF(kv);
    return err;
}

int
PyDict_DelItemString(PyObject *v, const char *key)
{
    PyObject *kv;
    int err;
    kv = PyUnicode_FromString(key);
    if (kv == NULL)
        return -1;
    err = PyDict_DelItem(v, kv);
    Py_DECREF(kv);
    return err;
}

/* Dictionary iterator types */

typedef struct {
    PyObject_HEAD
    PyDictObject *di_dict; /* Set to NULL when iterator is exhausted */
    Py_ssize_t di_used;
    Py_ssize_t di_pos;
    PyObject* di_result; /* reusable result tuple for iteritems */
    Py_ssize_t len;
} dictiterobject;

static PyObject *
dictiter_new(PyDictObject *dict, PyTypeObject *itertype)
{
    dictiterobject *di;
    di = PyObject_GC_New(dictiterobject, itertype);
    if (di == NULL)
        return NULL;
    Py_INCREF(dict);
    di->di_dict = dict;
    di->di_used = dict->ma_used;
    di->di_pos = 0;
    di->len = dict->ma_used;
    if (itertype == &PyDictIterItem_Type) {
        di->di_result = PyTuple_Pack(2, Py_None, Py_None);
        if (di->di_result == NULL) {
            Py_DECREF(di);
            return NULL;
        }
    }
    else
        di->di_result = NULL;
    _PyObject_GC_TRACK(di);
    return (PyObject *)di;
}

static void
dictiter_dealloc(dictiterobject *di)
{
    Py_XDECREF(di->di_dict);
    Py_XDECREF(di->di_result);
    PyObject_GC_Del(di);
}

static int
dictiter_traverse(dictiterobject *di, visitproc visit, void *arg)
{
    Py_VISIT(di->di_dict);
    Py_VISIT(di->di_result);
    return 0;
}

static PyObject *
dictiter_len(dictiterobject *di)
{
    Py_ssize_t len = 0;
    if (di->di_dict != NULL && di->di_used == di->di_dict->ma_used)
        len = di->len;
    return PyLong_FromSize_t(len);
}

PyDoc_STRVAR(length_hint_doc,
             "Private method returning an estimate of len(list(it)).");

static PyMethodDef dictiter_methods[] = {
    {"__length_hint__", (PyCFunction)dictiter_len, METH_NOARGS,
     length_hint_doc},
    {NULL,              NULL}           /* sentinel */
};

static PyObject *dictiter_iternextkey(dictiterobject *di)
{
    PyObject *key;
    register Py_ssize_t i, mask;
    register PyDictEntry *ep;
    PyDictObject *d = di->di_dict;

    if (d == NULL)
        return NULL;
    assert (PyDict_Check(d));

    if (di->di_used != d->ma_used) {
        PyErr_SetString(PyExc_RuntimeError,
                        "dictionary changed size during iteration");
        di->di_used = -1; /* Make this state sticky */
        return NULL;
    }

    i = di->di_pos;
    if (i < 0)
        goto fail;
    ep = d->ma_table;
    mask = d->ma_mask;
    while (i <= mask && ep[i].me_value == NULL)
        i++;
    di->di_pos = i+1;
    if (i > mask)
        goto fail;
    di->len--;
    key = ep[i].me_key;
    Py_INCREF(key);
    return key;

fail:
    Py_DECREF(d);
    di->di_dict = NULL;
    return NULL;
}

PyTypeObject PyDictIterKey_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "dict_keyiterator",                         /* tp_name */
    sizeof(dictiterobject),                     /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)dictiter_dealloc,               /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    0,                                          /* tp_repr */
    0,                                          /* tp_as_number */
    0,                                          /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)dictiter_traverse,            /* tp_traverse */
    0,                                          /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    PyObject_SelfIter,                          /* tp_iter */
    (iternextfunc)dictiter_iternextkey,         /* tp_iternext */
    dictiter_methods,                           /* tp_methods */
    0,
};

static PyObject *dictiter_iternextvalue(dictiterobject *di)
{
    PyObject *value;
    register Py_ssize_t i, mask;
    register PyDictEntry *ep;
    PyDictObject *d = di->di_dict;

    if (d == NULL)
        return NULL;
    assert (PyDict_Check(d));

    if (di->di_used != d->ma_used) {
        PyErr_SetString(PyExc_RuntimeError,
                        "dictionary changed size during iteration");
        di->di_used = -1; /* Make this state sticky */
        return NULL;
    }

    i = di->di_pos;
    mask = d->ma_mask;
    if (i < 0 || i > mask)
        goto fail;
    ep = d->ma_table;
    while ((value=ep[i].me_value) == NULL) {
        i++;
        if (i > mask)
            goto fail;
    }
    di->di_pos = i+1;
    di->len--;
    Py_INCREF(value);
    return value;

fail:
    Py_DECREF(d);
    di->di_dict = NULL;
    return NULL;
}

PyTypeObject PyDictIterValue_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "dict_valueiterator",                       /* tp_name */
    sizeof(dictiterobject),                     /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)dictiter_dealloc,               /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    0,                                          /* tp_repr */
    0,                                          /* tp_as_number */
    0,                                          /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)dictiter_traverse,            /* tp_traverse */
    0,                                          /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    PyObject_SelfIter,                          /* tp_iter */
    (iternextfunc)dictiter_iternextvalue,       /* tp_iternext */
    dictiter_methods,                           /* tp_methods */
    0,
};

static PyObject *dictiter_iternextitem(dictiterobject *di)
{
    PyObject *key, *value, *result = di->di_result;
    register Py_ssize_t i, mask;
    register PyDictEntry *ep;
    PyDictObject *d = di->di_dict;

    if (d == NULL)
        return NULL;
    assert (PyDict_Check(d));

    if (di->di_used != d->ma_used) {
        PyErr_SetString(PyExc_RuntimeError,
                        "dictionary changed size during iteration");
        di->di_used = -1; /* Make this state sticky */
        return NULL;
    }

    i = di->di_pos;
    if (i < 0)
        goto fail;
    ep = d->ma_table;
    mask = d->ma_mask;
    while (i <= mask && ep[i].me_value == NULL)
        i++;
    di->di_pos = i+1;
    if (i > mask)
        goto fail;

    if (result->ob_refcnt == 1) {
        Py_INCREF(result);
        Py_DECREF(PyTuple_GET_ITEM(result, 0));
        Py_DECREF(PyTuple_GET_ITEM(result, 1));
    } else {
        result = PyTuple_New(2);
        if (result == NULL)
            return NULL;
    }
    di->len--;
    key = ep[i].me_key;
    value = ep[i].me_value;
    Py_INCREF(key);
    Py_INCREF(value);
    PyTuple_SET_ITEM(result, 0, key);
    PyTuple_SET_ITEM(result, 1, value);
    return result;

fail:
    Py_DECREF(d);
    di->di_dict = NULL;
    return NULL;
}

PyTypeObject PyDictIterItem_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "dict_itemiterator",                        /* tp_name */
    sizeof(dictiterobject),                     /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)dictiter_dealloc,               /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    0,                                          /* tp_repr */
    0,                                          /* tp_as_number */
    0,                                          /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)dictiter_traverse,            /* tp_traverse */
    0,                                          /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    PyObject_SelfIter,                          /* tp_iter */
    (iternextfunc)dictiter_iternextitem,        /* tp_iternext */
    dictiter_methods,                           /* tp_methods */
    0,
};


/***********************************************/
/* View objects for keys(), items(), values(). */
/***********************************************/

/* The instance lay-out is the same for all three; but the type differs. */

typedef struct {
    PyObject_HEAD
    PyDictObject *dv_dict;
} dictviewobject;


static void
dictview_dealloc(dictviewobject *dv)
{
    Py_XDECREF(dv->dv_dict);
    PyObject_GC_Del(dv);
}

static int
dictview_traverse(dictviewobject *dv, visitproc visit, void *arg)
{
    Py_VISIT(dv->dv_dict);
    return 0;
}

static Py_ssize_t
dictview_len(dictviewobject *dv)
{
    Py_ssize_t len = 0;
    if (dv->dv_dict != NULL)
        len = dv->dv_dict->ma_used;
    return len;
}

static PyObject *
dictview_new(PyObject *dict, PyTypeObject *type)
{
    dictviewobject *dv;
    if (dict == NULL) {
        PyErr_BadInternalCall();
        return NULL;
    }
    if (!PyDict_Check(dict)) {
        /* XXX Get rid of this restriction later */
        PyErr_Format(PyExc_TypeError,
                     "%s() requires a dict argument, not '%s'",
                     type->tp_name, dict->ob_type->tp_name);
        return NULL;
    }
    dv = PyObject_GC_New(dictviewobject, type);
    if (dv == NULL)
        return NULL;
    Py_INCREF(dict);
    dv->dv_dict = (PyDictObject *)dict;
    _PyObject_GC_TRACK(dv);
    return (PyObject *)dv;
}

/* TODO(guido): The views objects are not complete:

 * support more set operations
 * support arbitrary mappings?
   - either these should be static or exported in dictobject.h
   - if public then they should probably be in builtins
*/

/* Return 1 if self is a subset of other, iterating over self;
   0 if not; -1 if an error occurred. */
static int
all_contained_in(PyObject *self, PyObject *other)
{
    PyObject *iter = PyObject_GetIter(self);
    int ok = 1;

    if (iter == NULL)
        return -1;
    for (;;) {
        PyObject *next = PyIter_Next(iter);
        if (next == NULL) {
            if (PyErr_Occurred())
                ok = -1;
            break;
        }
        ok = PySequence_Contains(other, next);
        Py_DECREF(next);
        if (ok <= 0)
            break;
    }
    Py_DECREF(iter);
    return ok;
}

static PyObject *
dictview_richcompare(PyObject *self, PyObject *other, int op)
{
    Py_ssize_t len_self, len_other;
    int ok;
    PyObject *result;

    assert(self != NULL);
    assert(PyDictViewSet_Check(self));
    assert(other != NULL);

    if (!PyAnySet_Check(other) && !PyDictViewSet_Check(other)) {
        Py_INCREF(Py_NotImplemented);
        return Py_NotImplemented;
    }

    len_self = PyObject_Size(self);
    if (len_self < 0)
        return NULL;
    len_other = PyObject_Size(other);
    if (len_other < 0)
        return NULL;

    ok = 0;
    switch(op) {

    case Py_NE:
    case Py_EQ:
        if (len_self == len_other)
            ok = all_contained_in(self, other);
        if (op == Py_NE && ok >= 0)
            ok = !ok;
        break;

    case Py_LT:
        if (len_self < len_other)
            ok = all_contained_in(self, other);
        break;

      case Py_LE:
          if (len_self <= len_other)
              ok = all_contained_in(self, other);
          break;

    case Py_GT:
        if (len_self > len_other)
            ok = all_contained_in(other, self);
        break;

    case Py_GE:
        if (len_self >= len_other)
            ok = all_contained_in(other, self);
        break;

    }
    if (ok < 0)
        return NULL;
    result = ok ? Py_True : Py_False;
    Py_INCREF(result);
    return result;
}

static PyObject *
dictview_repr(dictviewobject *dv)
{
    PyObject *seq;
    PyObject *result;

    seq = PySequence_List((PyObject *)dv);
    if (seq == NULL)
        return NULL;

    result = PyUnicode_FromFormat("%s(%R)", Py_TYPE(dv)->tp_name, seq);
    Py_DECREF(seq);
    return result;
}

/*** dict_keys ***/

static PyObject *
dictkeys_iter(dictviewobject *dv)
{
    if (dv->dv_dict == NULL) {
        Py_RETURN_NONE;
    }
    return dictiter_new(dv->dv_dict, &PyDictIterKey_Type);
}

static int
dictkeys_contains(dictviewobject *dv, PyObject *obj)
{
    if (dv->dv_dict == NULL)
        return 0;
    return PyDict_Contains((PyObject *)dv->dv_dict, obj);
}

static PySequenceMethods dictkeys_as_sequence = {
    (lenfunc)dictview_len,              /* sq_length */
    0,                                  /* sq_concat */
    0,                                  /* sq_repeat */
    0,                                  /* sq_item */
    0,                                  /* sq_slice */
    0,                                  /* sq_ass_item */
    0,                                  /* sq_ass_slice */
    (objobjproc)dictkeys_contains,      /* sq_contains */
};

static PyObject*
dictviews_sub(PyObject* self, PyObject *other)
{
    PyObject *result = PySet_New(self);
    PyObject *tmp;
    if (result == NULL)
        return NULL;

    tmp = PyObject_CallMethod(result, "difference_update", "O", other);
    if (tmp == NULL) {
        Py_DECREF(result);
        return NULL;
    }

    Py_DECREF(tmp);
    return result;
}

static PyObject*
dictviews_and(PyObject* self, PyObject *other)
{
    PyObject *result = PySet_New(self);
    PyObject *tmp;
    if (result == NULL)
        return NULL;

    tmp = PyObject_CallMethod(result, "intersection_update", "O", other);
    if (tmp == NULL) {
        Py_DECREF(result);
        return NULL;
    }

    Py_DECREF(tmp);
    return result;
}

static PyObject*
dictviews_or(PyObject* self, PyObject *other)
{
    PyObject *result = PySet_New(self);
    PyObject *tmp;
    if (result == NULL)
        return NULL;

    tmp = PyObject_CallMethod(result, "update", "O", other);
    if (tmp == NULL) {
        Py_DECREF(result);
        return NULL;
    }

    Py_DECREF(tmp);
    return result;
}

static PyObject*
dictviews_xor(PyObject* self, PyObject *other)
{
    PyObject *result = PySet_New(self);
    PyObject *tmp;
    if (result == NULL)
        return NULL;

    tmp = PyObject_CallMethod(result, "symmetric_difference_update", "O",
                              other);
    if (tmp == NULL) {
        Py_DECREF(result);
        return NULL;
    }

    Py_DECREF(tmp);
    return result;
}

static PyNumberMethods dictviews_as_number = {
    0,                                  /*nb_add*/
    (binaryfunc)dictviews_sub,          /*nb_subtract*/
    0,                                  /*nb_multiply*/
    0,                                  /*nb_remainder*/
    0,                                  /*nb_divmod*/
    0,                                  /*nb_power*/
    0,                                  /*nb_negative*/
    0,                                  /*nb_positive*/
    0,                                  /*nb_absolute*/
    0,                                  /*nb_bool*/
    0,                                  /*nb_invert*/
    0,                                  /*nb_lshift*/
    0,                                  /*nb_rshift*/
    (binaryfunc)dictviews_and,          /*nb_and*/
    (binaryfunc)dictviews_xor,          /*nb_xor*/
    (binaryfunc)dictviews_or,           /*nb_or*/
};

static PyMethodDef dictkeys_methods[] = {
    {NULL,              NULL}           /* sentinel */
};

PyTypeObject PyDictKeys_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "dict_keys",                                /* tp_name */
    sizeof(dictviewobject),                     /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)dictview_dealloc,               /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    (reprfunc)dictview_repr,                    /* tp_repr */
    &dictviews_as_number,                       /* tp_as_number */
    &dictkeys_as_sequence,                      /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)dictview_traverse,            /* tp_traverse */
    0,                                          /* tp_clear */
    dictview_richcompare,                       /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    (getiterfunc)dictkeys_iter,                 /* tp_iter */
    0,                                          /* tp_iternext */
    dictkeys_methods,                           /* tp_methods */
    0,
};

static PyObject *
dictkeys_new(PyObject *dict)
{
    return dictview_new(dict, &PyDictKeys_Type);
}

/*** dict_items ***/

static PyObject *
dictitems_iter(dictviewobject *dv)
{
    if (dv->dv_dict == NULL) {
        Py_RETURN_NONE;
    }
    return dictiter_new(dv->dv_dict, &PyDictIterItem_Type);
}

static int
dictitems_contains(dictviewobject *dv, PyObject *obj)
{
    PyObject *key, *value, *found;
    if (dv->dv_dict == NULL)
        return 0;
    if (!PyTuple_Check(obj) || PyTuple_GET_SIZE(obj) != 2)
        return 0;
    key = PyTuple_GET_ITEM(obj, 0);
    value = PyTuple_GET_ITEM(obj, 1);
    found = PyDict_GetItem((PyObject *)dv->dv_dict, key);
    if (found == NULL) {
        if (PyErr_Occurred())
            return -1;
        return 0;
    }
    return PyObject_RichCompareBool(value, found, Py_EQ);
}

static PySequenceMethods dictitems_as_sequence = {
    (lenfunc)dictview_len,              /* sq_length */
    0,                                  /* sq_concat */
    0,                                  /* sq_repeat */
    0,                                  /* sq_item */
    0,                                  /* sq_slice */
    0,                                  /* sq_ass_item */
    0,                                  /* sq_ass_slice */
    (objobjproc)dictitems_contains,     /* sq_contains */
};

static PyMethodDef dictitems_methods[] = {
    {NULL,              NULL}           /* sentinel */
};

PyTypeObject PyDictItems_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "dict_items",                               /* tp_name */
    sizeof(dictviewobject),                     /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)dictview_dealloc,               /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    (reprfunc)dictview_repr,                    /* tp_repr */
    &dictviews_as_number,                       /* tp_as_number */
    &dictitems_as_sequence,                     /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)dictview_traverse,            /* tp_traverse */
    0,                                          /* tp_clear */
    dictview_richcompare,                       /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    (getiterfunc)dictitems_iter,                /* tp_iter */
    0,                                          /* tp_iternext */
    dictitems_methods,                          /* tp_methods */
    0,
};

static PyObject *
dictitems_new(PyObject *dict)
{
    return dictview_new(dict, &PyDictItems_Type);
}

/*** dict_values ***/

static PyObject *
dictvalues_iter(dictviewobject *dv)
{
    if (dv->dv_dict == NULL) {
        Py_RETURN_NONE;
    }
    return dictiter_new(dv->dv_dict, &PyDictIterValue_Type);
}

static PySequenceMethods dictvalues_as_sequence = {
    (lenfunc)dictview_len,              /* sq_length */
    0,                                  /* sq_concat */
    0,                                  /* sq_repeat */
    0,                                  /* sq_item */
    0,                                  /* sq_slice */
    0,                                  /* sq_ass_item */
    0,                                  /* sq_ass_slice */
    (objobjproc)0,                      /* sq_contains */
};

static PyMethodDef dictvalues_methods[] = {
    {NULL,              NULL}           /* sentinel */
};

PyTypeObject PyDictValues_Type = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "dict_values",                              /* tp_name */
    sizeof(dictviewobject),                     /* tp_basicsize */
    0,                                          /* tp_itemsize */
    /* methods */
    (destructor)dictview_dealloc,               /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    (reprfunc)dictview_repr,                    /* tp_repr */
    0,                                          /* tp_as_number */
    &dictvalues_as_sequence,                    /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    PyObject_GenericGetAttr,                    /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
    0,                                          /* tp_doc */
    (traverseproc)dictview_traverse,            /* tp_traverse */
    0,                                          /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    (getiterfunc)dictvalues_iter,               /* tp_iter */
    0,                                          /* tp_iternext */
    dictvalues_methods,                         /* tp_methods */
    0,
};

static PyObject *
dictvalues_new(PyObject *dict)
{
    return dictview_new(dict, &PyDictValues_Type);
}
Tip: Filter by directory path e.g. /media app.js to search for public/media/app.js.
Tip: Use camelCasing e.g. ProjME to search for ProjectModifiedEvent.java.
Tip: Filter by extension type e.g. /repo .js to search for all .js files in the /repo directory.
Tip: Separate your search with spaces e.g. /ssh pom.xml to search for src/ssh/pom.xml.
Tip: Use ↑ and ↓ arrow keys to navigate and return to view the file.
Tip: You can also navigate files with Ctrl+j (next) and Ctrl+k (previous) and view the file with Ctrl+o.
Tip: You can also navigate files with Alt+j (next) and Alt+k (previous) and view the file with Alt+o.