Source

cpython-withatomic / Lib / difflib.py

   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
#! /usr/bin/env python3

"""
Module difflib -- helpers for computing deltas between objects.

Function get_close_matches(word, possibilities, n=3, cutoff=0.6):
    Use SequenceMatcher to return list of the best "good enough" matches.

Function context_diff(a, b):
    For two lists of strings, return a delta in context diff format.

Function ndiff(a, b):
    Return a delta: the difference between `a` and `b` (lists of strings).

Function restore(delta, which):
    Return one of the two sequences that generated an ndiff delta.

Function unified_diff(a, b):
    For two lists of strings, return a delta in unified diff format.

Class SequenceMatcher:
    A flexible class for comparing pairs of sequences of any type.

Class Differ:
    For producing human-readable deltas from sequences of lines of text.

Class HtmlDiff:
    For producing HTML side by side comparison with change highlights.
"""

__all__ = ['get_close_matches', 'ndiff', 'restore', 'SequenceMatcher',
           'Differ','IS_CHARACTER_JUNK', 'IS_LINE_JUNK', 'context_diff',
           'unified_diff', 'HtmlDiff', 'Match']

import warnings
import heapq
from collections import namedtuple as _namedtuple

Match = _namedtuple('Match', 'a b size')

def _calculate_ratio(matches, length):
    if length:
        return 2.0 * matches / length
    return 1.0

class SequenceMatcher:

    """
    SequenceMatcher is a flexible class for comparing pairs of sequences of
    any type, so long as the sequence elements are hashable.  The basic
    algorithm predates, and is a little fancier than, an algorithm
    published in the late 1980's by Ratcliff and Obershelp under the
    hyperbolic name "gestalt pattern matching".  The basic idea is to find
    the longest contiguous matching subsequence that contains no "junk"
    elements (R-O doesn't address junk).  The same idea is then applied
    recursively to the pieces of the sequences to the left and to the right
    of the matching subsequence.  This does not yield minimal edit
    sequences, but does tend to yield matches that "look right" to people.

    SequenceMatcher tries to compute a "human-friendly diff" between two
    sequences.  Unlike e.g. UNIX(tm) diff, the fundamental notion is the
    longest *contiguous* & junk-free matching subsequence.  That's what
    catches peoples' eyes.  The Windows(tm) windiff has another interesting
    notion, pairing up elements that appear uniquely in each sequence.
    That, and the method here, appear to yield more intuitive difference
    reports than does diff.  This method appears to be the least vulnerable
    to synching up on blocks of "junk lines", though (like blank lines in
    ordinary text files, or maybe "<P>" lines in HTML files).  That may be
    because this is the only method of the 3 that has a *concept* of
    "junk" <wink>.

    Example, comparing two strings, and considering blanks to be "junk":

    >>> s = SequenceMatcher(lambda x: x == " ",
    ...                     "private Thread currentThread;",
    ...                     "private volatile Thread currentThread;")
    >>>

    .ratio() returns a float in [0, 1], measuring the "similarity" of the
    sequences.  As a rule of thumb, a .ratio() value over 0.6 means the
    sequences are close matches:

    >>> print(round(s.ratio(), 3))
    0.866
    >>>

    If you're only interested in where the sequences match,
    .get_matching_blocks() is handy:

    >>> for block in s.get_matching_blocks():
    ...     print("a[%d] and b[%d] match for %d elements" % block)
    a[0] and b[0] match for 8 elements
    a[8] and b[17] match for 21 elements
    a[29] and b[38] match for 0 elements

    Note that the last tuple returned by .get_matching_blocks() is always a
    dummy, (len(a), len(b), 0), and this is the only case in which the last
    tuple element (number of elements matched) is 0.

    If you want to know how to change the first sequence into the second,
    use .get_opcodes():

    >>> for opcode in s.get_opcodes():
    ...     print("%6s a[%d:%d] b[%d:%d]" % opcode)
     equal a[0:8] b[0:8]
    insert a[8:8] b[8:17]
     equal a[8:29] b[17:38]

    See the Differ class for a fancy human-friendly file differencer, which
    uses SequenceMatcher both to compare sequences of lines, and to compare
    sequences of characters within similar (near-matching) lines.

    See also function get_close_matches() in this module, which shows how
    simple code building on SequenceMatcher can be used to do useful work.

    Timing:  Basic R-O is cubic time worst case and quadratic time expected
    case.  SequenceMatcher is quadratic time for the worst case and has
    expected-case behavior dependent in a complicated way on how many
    elements the sequences have in common; best case time is linear.

    Methods:

    __init__(isjunk=None, a='', b='')
        Construct a SequenceMatcher.

    set_seqs(a, b)
        Set the two sequences to be compared.

    set_seq1(a)
        Set the first sequence to be compared.

    set_seq2(b)
        Set the second sequence to be compared.

    find_longest_match(alo, ahi, blo, bhi)
        Find longest matching block in a[alo:ahi] and b[blo:bhi].

    get_matching_blocks()
        Return list of triples describing matching subsequences.

    get_opcodes()
        Return list of 5-tuples describing how to turn a into b.

    ratio()
        Return a measure of the sequences' similarity (float in [0,1]).

    quick_ratio()
        Return an upper bound on .ratio() relatively quickly.

    real_quick_ratio()
        Return an upper bound on ratio() very quickly.
    """

    def __init__(self, isjunk=None, a='', b='', autojunk=True):
        """Construct a SequenceMatcher.

        Optional arg isjunk is None (the default), or a one-argument
        function that takes a sequence element and returns true iff the
        element is junk.  None is equivalent to passing "lambda x: 0", i.e.
        no elements are considered to be junk.  For example, pass
            lambda x: x in " \\t"
        if you're comparing lines as sequences of characters, and don't
        want to synch up on blanks or hard tabs.

        Optional arg a is the first of two sequences to be compared.  By
        default, an empty string.  The elements of a must be hashable.  See
        also .set_seqs() and .set_seq1().

        Optional arg b is the second of two sequences to be compared.  By
        default, an empty string.  The elements of b must be hashable. See
        also .set_seqs() and .set_seq2().

        Optional arg autojunk should be set to False to disable the
        "automatic junk heuristic" that treats popular elements as junk
        (see module documentation for more information).
        """

        # Members:
        # a
        #      first sequence
        # b
        #      second sequence; differences are computed as "what do
        #      we need to do to 'a' to change it into 'b'?"
        # b2j
        #      for x in b, b2j[x] is a list of the indices (into b)
        #      at which x appears; junk and popular elements do not appear
        # fullbcount
        #      for x in b, fullbcount[x] == the number of times x
        #      appears in b; only materialized if really needed (used
        #      only for computing quick_ratio())
        # matching_blocks
        #      a list of (i, j, k) triples, where a[i:i+k] == b[j:j+k];
        #      ascending & non-overlapping in i and in j; terminated by
        #      a dummy (len(a), len(b), 0) sentinel
        # opcodes
        #      a list of (tag, i1, i2, j1, j2) tuples, where tag is
        #      one of
        #          'replace'   a[i1:i2] should be replaced by b[j1:j2]
        #          'delete'    a[i1:i2] should be deleted
        #          'insert'    b[j1:j2] should be inserted
        #          'equal'     a[i1:i2] == b[j1:j2]
        # isjunk
        #      a user-supplied function taking a sequence element and
        #      returning true iff the element is "junk" -- this has
        #      subtle but helpful effects on the algorithm, which I'll
        #      get around to writing up someday <0.9 wink>.
        #      DON'T USE!  Only __chain_b uses this.  Use isbjunk.
        # bjunk
        #      the items in b for which isjunk is True.
        # bpopular
        #      nonjunk items in b treated as junk by the heuristic (if used).

        self.isjunk = isjunk
        self.a = self.b = None
        self.autojunk = autojunk
        self.set_seqs(a, b)

    def set_seqs(self, a, b):
        """Set the two sequences to be compared.

        >>> s = SequenceMatcher()
        >>> s.set_seqs("abcd", "bcde")
        >>> s.ratio()
        0.75
        """

        self.set_seq1(a)
        self.set_seq2(b)

    def set_seq1(self, a):
        """Set the first sequence to be compared.

        The second sequence to be compared is not changed.

        >>> s = SequenceMatcher(None, "abcd", "bcde")
        >>> s.ratio()
        0.75
        >>> s.set_seq1("bcde")
        >>> s.ratio()
        1.0
        >>>

        SequenceMatcher computes and caches detailed information about the
        second sequence, so if you want to compare one sequence S against
        many sequences, use .set_seq2(S) once and call .set_seq1(x)
        repeatedly for each of the other sequences.

        See also set_seqs() and set_seq2().
        """

        if a is self.a:
            return
        self.a = a
        self.matching_blocks = self.opcodes = None

    def set_seq2(self, b):
        """Set the second sequence to be compared.

        The first sequence to be compared is not changed.

        >>> s = SequenceMatcher(None, "abcd", "bcde")
        >>> s.ratio()
        0.75
        >>> s.set_seq2("abcd")
        >>> s.ratio()
        1.0
        >>>

        SequenceMatcher computes and caches detailed information about the
        second sequence, so if you want to compare one sequence S against
        many sequences, use .set_seq2(S) once and call .set_seq1(x)
        repeatedly for each of the other sequences.

        See also set_seqs() and set_seq1().
        """

        if b is self.b:
            return
        self.b = b
        self.matching_blocks = self.opcodes = None
        self.fullbcount = None
        self.__chain_b()

    # For each element x in b, set b2j[x] to a list of the indices in
    # b where x appears; the indices are in increasing order; note that
    # the number of times x appears in b is len(b2j[x]) ...
    # when self.isjunk is defined, junk elements don't show up in this
    # map at all, which stops the central find_longest_match method
    # from starting any matching block at a junk element ...
    # also creates the fast isbjunk function ...
    # b2j also does not contain entries for "popular" elements, meaning
    # elements that account for more than 1 + 1% of the total elements, and
    # when the sequence is reasonably large (>= 200 elements); this can
    # be viewed as an adaptive notion of semi-junk, and yields an enormous
    # speedup when, e.g., comparing program files with hundreds of
    # instances of "return NULL;" ...
    # note that this is only called when b changes; so for cross-product
    # kinds of matches, it's best to call set_seq2 once, then set_seq1
    # repeatedly

    def __chain_b(self):
        # Because isjunk is a user-defined (not C) function, and we test
        # for junk a LOT, it's important to minimize the number of calls.
        # Before the tricks described here, __chain_b was by far the most
        # time-consuming routine in the whole module!  If anyone sees
        # Jim Roskind, thank him again for profile.py -- I never would
        # have guessed that.
        # The first trick is to build b2j ignoring the possibility
        # of junk.  I.e., we don't call isjunk at all yet.  Throwing
        # out the junk later is much cheaper than building b2j "right"
        # from the start.
        b = self.b
        self.b2j = b2j = {}

        for i, elt in enumerate(b):
            indices = b2j.setdefault(elt, [])
            indices.append(i)

        # Purge junk elements
        self.bjunk = junk = set()
        isjunk = self.isjunk
        if isjunk:
            for elt in b2j.keys():
                if isjunk(elt):
                    junk.add(elt)
            for elt in junk: # separate loop avoids separate list of keys
                del b2j[elt]

        # Purge popular elements that are not junk
        self.bpopular = popular = set()
        n = len(b)
        if self.autojunk and n >= 200:
            ntest = n // 100 + 1
            for elt, idxs in b2j.items():
                if len(idxs) > ntest:
                    popular.add(elt)
            for elt in popular: # ditto; as fast for 1% deletion
                del b2j[elt]

    def isbjunk(self, item):
        "Deprecated; use 'item in SequenceMatcher().bjunk'."
        warnings.warn("'SequenceMatcher().isbjunk(item)' is deprecated;\n"
                      "use 'item in SMinstance.bjunk' instead.",
                      DeprecationWarning, 2)
        return item in self.bjunk

    def isbpopular(self, item):
        "Deprecated; use 'item in SequenceMatcher().bpopular'."
        warnings.warn("'SequenceMatcher().isbpopular(item)' is deprecated;\n"
                      "use 'item in SMinstance.bpopular' instead.",
                      DeprecationWarning, 2)
        return item in self.bpopular

    def find_longest_match(self, alo, ahi, blo, bhi):
        """Find longest matching block in a[alo:ahi] and b[blo:bhi].

        If isjunk is not defined:

        Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where
            alo <= i <= i+k <= ahi
            blo <= j <= j+k <= bhi
        and for all (i',j',k') meeting those conditions,
            k >= k'
            i <= i'
            and if i == i', j <= j'

        In other words, of all maximal matching blocks, return one that
        starts earliest in a, and of all those maximal matching blocks that
        start earliest in a, return the one that starts earliest in b.

        >>> s = SequenceMatcher(None, " abcd", "abcd abcd")
        >>> s.find_longest_match(0, 5, 0, 9)
        Match(a=0, b=4, size=5)

        If isjunk is defined, first the longest matching block is
        determined as above, but with the additional restriction that no
        junk element appears in the block.  Then that block is extended as
        far as possible by matching (only) junk elements on both sides.  So
        the resulting block never matches on junk except as identical junk
        happens to be adjacent to an "interesting" match.

        Here's the same example as before, but considering blanks to be
        junk.  That prevents " abcd" from matching the " abcd" at the tail
        end of the second sequence directly.  Instead only the "abcd" can
        match, and matches the leftmost "abcd" in the second sequence:

        >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd")
        >>> s.find_longest_match(0, 5, 0, 9)
        Match(a=1, b=0, size=4)

        If no blocks match, return (alo, blo, 0).

        >>> s = SequenceMatcher(None, "ab", "c")
        >>> s.find_longest_match(0, 2, 0, 1)
        Match(a=0, b=0, size=0)
        """

        # CAUTION:  stripping common prefix or suffix would be incorrect.
        # E.g.,
        #    ab
        #    acab
        # Longest matching block is "ab", but if common prefix is
        # stripped, it's "a" (tied with "b").  UNIX(tm) diff does so
        # strip, so ends up claiming that ab is changed to acab by
        # inserting "ca" in the middle.  That's minimal but unintuitive:
        # "it's obvious" that someone inserted "ac" at the front.
        # Windiff ends up at the same place as diff, but by pairing up
        # the unique 'b's and then matching the first two 'a's.

        a, b, b2j, isbjunk = self.a, self.b, self.b2j, self.bjunk.__contains__
        besti, bestj, bestsize = alo, blo, 0
        # find longest junk-free match
        # during an iteration of the loop, j2len[j] = length of longest
        # junk-free match ending with a[i-1] and b[j]
        j2len = {}
        nothing = []
        for i in range(alo, ahi):
            # look at all instances of a[i] in b; note that because
            # b2j has no junk keys, the loop is skipped if a[i] is junk
            j2lenget = j2len.get
            newj2len = {}
            for j in b2j.get(a[i], nothing):
                # a[i] matches b[j]
                if j < blo:
                    continue
                if j >= bhi:
                    break
                k = newj2len[j] = j2lenget(j-1, 0) + 1
                if k > bestsize:
                    besti, bestj, bestsize = i-k+1, j-k+1, k
            j2len = newj2len

        # Extend the best by non-junk elements on each end.  In particular,
        # "popular" non-junk elements aren't in b2j, which greatly speeds
        # the inner loop above, but also means "the best" match so far
        # doesn't contain any junk *or* popular non-junk elements.
        while besti > alo and bestj > blo and \
              not isbjunk(b[bestj-1]) and \
              a[besti-1] == b[bestj-1]:
            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
        while besti+bestsize < ahi and bestj+bestsize < bhi and \
              not isbjunk(b[bestj+bestsize]) and \
              a[besti+bestsize] == b[bestj+bestsize]:
            bestsize += 1

        # Now that we have a wholly interesting match (albeit possibly
        # empty!), we may as well suck up the matching junk on each
        # side of it too.  Can't think of a good reason not to, and it
        # saves post-processing the (possibly considerable) expense of
        # figuring out what to do with it.  In the case of an empty
        # interesting match, this is clearly the right thing to do,
        # because no other kind of match is possible in the regions.
        while besti > alo and bestj > blo and \
              isbjunk(b[bestj-1]) and \
              a[besti-1] == b[bestj-1]:
            besti, bestj, bestsize = besti-1, bestj-1, bestsize+1
        while besti+bestsize < ahi and bestj+bestsize < bhi and \
              isbjunk(b[bestj+bestsize]) and \
              a[besti+bestsize] == b[bestj+bestsize]:
            bestsize = bestsize + 1

        return Match(besti, bestj, bestsize)

    def get_matching_blocks(self):
        """Return list of triples describing matching subsequences.

        Each triple is of the form (i, j, n), and means that
        a[i:i+n] == b[j:j+n].  The triples are monotonically increasing in
        i and in j.  New in Python 2.5, it's also guaranteed that if
        (i, j, n) and (i', j', n') are adjacent triples in the list, and
        the second is not the last triple in the list, then i+n != i' or
        j+n != j'.  IOW, adjacent triples never describe adjacent equal
        blocks.

        The last triple is a dummy, (len(a), len(b), 0), and is the only
        triple with n==0.

        >>> s = SequenceMatcher(None, "abxcd", "abcd")
        >>> list(s.get_matching_blocks())
        [Match(a=0, b=0, size=2), Match(a=3, b=2, size=2), Match(a=5, b=4, size=0)]
        """

        if self.matching_blocks is not None:
            return self.matching_blocks
        la, lb = len(self.a), len(self.b)

        # This is most naturally expressed as a recursive algorithm, but
        # at least one user bumped into extreme use cases that exceeded
        # the recursion limit on their box.  So, now we maintain a list
        # ('queue`) of blocks we still need to look at, and append partial
        # results to `matching_blocks` in a loop; the matches are sorted
        # at the end.
        queue = [(0, la, 0, lb)]
        matching_blocks = []
        while queue:
            alo, ahi, blo, bhi = queue.pop()
            i, j, k = x = self.find_longest_match(alo, ahi, blo, bhi)
            # a[alo:i] vs b[blo:j] unknown
            # a[i:i+k] same as b[j:j+k]
            # a[i+k:ahi] vs b[j+k:bhi] unknown
            if k:   # if k is 0, there was no matching block
                matching_blocks.append(x)
                if alo < i and blo < j:
                    queue.append((alo, i, blo, j))
                if i+k < ahi and j+k < bhi:
                    queue.append((i+k, ahi, j+k, bhi))
        matching_blocks.sort()

        # It's possible that we have adjacent equal blocks in the
        # matching_blocks list now.  Starting with 2.5, this code was added
        # to collapse them.
        i1 = j1 = k1 = 0
        non_adjacent = []
        for i2, j2, k2 in matching_blocks:
            # Is this block adjacent to i1, j1, k1?
            if i1 + k1 == i2 and j1 + k1 == j2:
                # Yes, so collapse them -- this just increases the length of
                # the first block by the length of the second, and the first
                # block so lengthened remains the block to compare against.
                k1 += k2
            else:
                # Not adjacent.  Remember the first block (k1==0 means it's
                # the dummy we started with), and make the second block the
                # new block to compare against.
                if k1:
                    non_adjacent.append((i1, j1, k1))
                i1, j1, k1 = i2, j2, k2
        if k1:
            non_adjacent.append((i1, j1, k1))

        non_adjacent.append( (la, lb, 0) )
        self.matching_blocks = non_adjacent
        return map(Match._make, self.matching_blocks)

    def get_opcodes(self):
        """Return list of 5-tuples describing how to turn a into b.

        Each tuple is of the form (tag, i1, i2, j1, j2).  The first tuple
        has i1 == j1 == 0, and remaining tuples have i1 == the i2 from the
        tuple preceding it, and likewise for j1 == the previous j2.

        The tags are strings, with these meanings:

        'replace':  a[i1:i2] should be replaced by b[j1:j2]
        'delete':   a[i1:i2] should be deleted.
                    Note that j1==j2 in this case.
        'insert':   b[j1:j2] should be inserted at a[i1:i1].
                    Note that i1==i2 in this case.
        'equal':    a[i1:i2] == b[j1:j2]

        >>> a = "qabxcd"
        >>> b = "abycdf"
        >>> s = SequenceMatcher(None, a, b)
        >>> for tag, i1, i2, j1, j2 in s.get_opcodes():
        ...    print(("%7s a[%d:%d] (%s) b[%d:%d] (%s)" %
        ...           (tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2])))
         delete a[0:1] (q) b[0:0] ()
          equal a[1:3] (ab) b[0:2] (ab)
        replace a[3:4] (x) b[2:3] (y)
          equal a[4:6] (cd) b[3:5] (cd)
         insert a[6:6] () b[5:6] (f)
        """

        if self.opcodes is not None:
            return self.opcodes
        i = j = 0
        self.opcodes = answer = []
        for ai, bj, size in self.get_matching_blocks():
            # invariant:  we've pumped out correct diffs to change
            # a[:i] into b[:j], and the next matching block is
            # a[ai:ai+size] == b[bj:bj+size].  So we need to pump
            # out a diff to change a[i:ai] into b[j:bj], pump out
            # the matching block, and move (i,j) beyond the match
            tag = ''
            if i < ai and j < bj:
                tag = 'replace'
            elif i < ai:
                tag = 'delete'
            elif j < bj:
                tag = 'insert'
            if tag:
                answer.append( (tag, i, ai, j, bj) )
            i, j = ai+size, bj+size
            # the list of matching blocks is terminated by a
            # sentinel with size 0
            if size:
                answer.append( ('equal', ai, i, bj, j) )
        return answer

    def get_grouped_opcodes(self, n=3):
        """ Isolate change clusters by eliminating ranges with no changes.

        Return a generator of groups with upto n lines of context.
        Each group is in the same format as returned by get_opcodes().

        >>> from pprint import pprint
        >>> a = list(map(str, range(1,40)))
        >>> b = a[:]
        >>> b[8:8] = ['i']     # Make an insertion
        >>> b[20] += 'x'       # Make a replacement
        >>> b[23:28] = []      # Make a deletion
        >>> b[30] += 'y'       # Make another replacement
        >>> pprint(list(SequenceMatcher(None,a,b).get_grouped_opcodes()))
        [[('equal', 5, 8, 5, 8), ('insert', 8, 8, 8, 9), ('equal', 8, 11, 9, 12)],
         [('equal', 16, 19, 17, 20),
          ('replace', 19, 20, 20, 21),
          ('equal', 20, 22, 21, 23),
          ('delete', 22, 27, 23, 23),
          ('equal', 27, 30, 23, 26)],
         [('equal', 31, 34, 27, 30),
          ('replace', 34, 35, 30, 31),
          ('equal', 35, 38, 31, 34)]]
        """

        codes = self.get_opcodes()
        if not codes:
            codes = [("equal", 0, 1, 0, 1)]
        # Fixup leading and trailing groups if they show no changes.
        if codes[0][0] == 'equal':
            tag, i1, i2, j1, j2 = codes[0]
            codes[0] = tag, max(i1, i2-n), i2, max(j1, j2-n), j2
        if codes[-1][0] == 'equal':
            tag, i1, i2, j1, j2 = codes[-1]
            codes[-1] = tag, i1, min(i2, i1+n), j1, min(j2, j1+n)

        nn = n + n
        group = []
        for tag, i1, i2, j1, j2 in codes:
            # End the current group and start a new one whenever
            # there is a large range with no changes.
            if tag == 'equal' and i2-i1 > nn:
                group.append((tag, i1, min(i2, i1+n), j1, min(j2, j1+n)))
                yield group
                group = []
                i1, j1 = max(i1, i2-n), max(j1, j2-n)
            group.append((tag, i1, i2, j1 ,j2))
        if group and not (len(group)==1 and group[0][0] == 'equal'):
            yield group

    def ratio(self):
        """Return a measure of the sequences' similarity (float in [0,1]).

        Where T is the total number of elements in both sequences, and
        M is the number of matches, this is 2.0*M / T.
        Note that this is 1 if the sequences are identical, and 0 if
        they have nothing in common.

        .ratio() is expensive to compute if you haven't already computed
        .get_matching_blocks() or .get_opcodes(), in which case you may
        want to try .quick_ratio() or .real_quick_ratio() first to get an
        upper bound.

        >>> s = SequenceMatcher(None, "abcd", "bcde")
        >>> s.ratio()
        0.75
        >>> s.quick_ratio()
        0.75
        >>> s.real_quick_ratio()
        1.0
        """

        matches = sum(triple[-1] for triple in self.get_matching_blocks())
        return _calculate_ratio(matches, len(self.a) + len(self.b))

    def quick_ratio(self):
        """Return an upper bound on ratio() relatively quickly.

        This isn't defined beyond that it is an upper bound on .ratio(), and
        is faster to compute.
        """

        # viewing a and b as multisets, set matches to the cardinality
        # of their intersection; this counts the number of matches
        # without regard to order, so is clearly an upper bound
        if self.fullbcount is None:
            self.fullbcount = fullbcount = {}
            for elt in self.b:
                fullbcount[elt] = fullbcount.get(elt, 0) + 1
        fullbcount = self.fullbcount
        # avail[x] is the number of times x appears in 'b' less the
        # number of times we've seen it in 'a' so far ... kinda
        avail = {}
        availhas, matches = avail.__contains__, 0
        for elt in self.a:
            if availhas(elt):
                numb = avail[elt]
            else:
                numb = fullbcount.get(elt, 0)
            avail[elt] = numb - 1
            if numb > 0:
                matches = matches + 1
        return _calculate_ratio(matches, len(self.a) + len(self.b))

    def real_quick_ratio(self):
        """Return an upper bound on ratio() very quickly.

        This isn't defined beyond that it is an upper bound on .ratio(), and
        is faster to compute than either .ratio() or .quick_ratio().
        """

        la, lb = len(self.a), len(self.b)
        # can't have more matches than the number of elements in the
        # shorter sequence
        return _calculate_ratio(min(la, lb), la + lb)

def get_close_matches(word, possibilities, n=3, cutoff=0.6):
    """Use SequenceMatcher to return list of the best "good enough" matches.

    word is a sequence for which close matches are desired (typically a
    string).

    possibilities is a list of sequences against which to match word
    (typically a list of strings).

    Optional arg n (default 3) is the maximum number of close matches to
    return.  n must be > 0.

    Optional arg cutoff (default 0.6) is a float in [0, 1].  Possibilities
    that don't score at least that similar to word are ignored.

    The best (no more than n) matches among the possibilities are returned
    in a list, sorted by similarity score, most similar first.

    >>> get_close_matches("appel", ["ape", "apple", "peach", "puppy"])
    ['apple', 'ape']
    >>> import keyword as _keyword
    >>> get_close_matches("wheel", _keyword.kwlist)
    ['while']
    >>> get_close_matches("Apple", _keyword.kwlist)
    []
    >>> get_close_matches("accept", _keyword.kwlist)
    ['except']
    """

    if not n >  0:
        raise ValueError("n must be > 0: %r" % (n,))
    if not 0.0 <= cutoff <= 1.0:
        raise ValueError("cutoff must be in [0.0, 1.0]: %r" % (cutoff,))
    result = []
    s = SequenceMatcher()
    s.set_seq2(word)
    for x in possibilities:
        s.set_seq1(x)
        if s.real_quick_ratio() >= cutoff and \
           s.quick_ratio() >= cutoff and \
           s.ratio() >= cutoff:
            result.append((s.ratio(), x))

    # Move the best scorers to head of list
    result = heapq.nlargest(n, result)
    # Strip scores for the best n matches
    return [x for score, x in result]

def _count_leading(line, ch):
    """
    Return number of `ch` characters at the start of `line`.

    Example:

    >>> _count_leading('   abc', ' ')
    3
    """

    i, n = 0, len(line)
    while i < n and line[i] == ch:
        i += 1
    return i

class Differ:
    r"""
    Differ is a class for comparing sequences of lines of text, and
    producing human-readable differences or deltas.  Differ uses
    SequenceMatcher both to compare sequences of lines, and to compare
    sequences of characters within similar (near-matching) lines.

    Each line of a Differ delta begins with a two-letter code:

        '- '    line unique to sequence 1
        '+ '    line unique to sequence 2
        '  '    line common to both sequences
        '? '    line not present in either input sequence

    Lines beginning with '? ' attempt to guide the eye to intraline
    differences, and were not present in either input sequence.  These lines
    can be confusing if the sequences contain tab characters.

    Note that Differ makes no claim to produce a *minimal* diff.  To the
    contrary, minimal diffs are often counter-intuitive, because they synch
    up anywhere possible, sometimes accidental matches 100 pages apart.
    Restricting synch points to contiguous matches preserves some notion of
    locality, at the occasional cost of producing a longer diff.

    Example: Comparing two texts.

    First we set up the texts, sequences of individual single-line strings
    ending with newlines (such sequences can also be obtained from the
    `readlines()` method of file-like objects):

    >>> text1 = '''  1. Beautiful is better than ugly.
    ...   2. Explicit is better than implicit.
    ...   3. Simple is better than complex.
    ...   4. Complex is better than complicated.
    ... '''.splitlines(1)
    >>> len(text1)
    4
    >>> text1[0][-1]
    '\n'
    >>> text2 = '''  1. Beautiful is better than ugly.
    ...   3.   Simple is better than complex.
    ...   4. Complicated is better than complex.
    ...   5. Flat is better than nested.
    ... '''.splitlines(1)

    Next we instantiate a Differ object:

    >>> d = Differ()

    Note that when instantiating a Differ object we may pass functions to
    filter out line and character 'junk'.  See Differ.__init__ for details.

    Finally, we compare the two:

    >>> result = list(d.compare(text1, text2))

    'result' is a list of strings, so let's pretty-print it:

    >>> from pprint import pprint as _pprint
    >>> _pprint(result)
    ['    1. Beautiful is better than ugly.\n',
     '-   2. Explicit is better than implicit.\n',
     '-   3. Simple is better than complex.\n',
     '+   3.   Simple is better than complex.\n',
     '?     ++\n',
     '-   4. Complex is better than complicated.\n',
     '?            ^                     ---- ^\n',
     '+   4. Complicated is better than complex.\n',
     '?           ++++ ^                      ^\n',
     '+   5. Flat is better than nested.\n']

    As a single multi-line string it looks like this:

    >>> print(''.join(result), end="")
        1. Beautiful is better than ugly.
    -   2. Explicit is better than implicit.
    -   3. Simple is better than complex.
    +   3.   Simple is better than complex.
    ?     ++
    -   4. Complex is better than complicated.
    ?            ^                     ---- ^
    +   4. Complicated is better than complex.
    ?           ++++ ^                      ^
    +   5. Flat is better than nested.

    Methods:

    __init__(linejunk=None, charjunk=None)
        Construct a text differencer, with optional filters.

    compare(a, b)
        Compare two sequences of lines; generate the resulting delta.
    """

    def __init__(self, linejunk=None, charjunk=None):
        """
        Construct a text differencer, with optional filters.

        The two optional keyword parameters are for filter functions:

        - `linejunk`: A function that should accept a single string argument,
          and return true iff the string is junk. The module-level function
          `IS_LINE_JUNK` may be used to filter out lines without visible
          characters, except for at most one splat ('#').  It is recommended
          to leave linejunk None; as of Python 2.3, the underlying
          SequenceMatcher class has grown an adaptive notion of "noise" lines
          that's better than any static definition the author has ever been
          able to craft.

        - `charjunk`: A function that should accept a string of length 1. The
          module-level function `IS_CHARACTER_JUNK` may be used to filter out
          whitespace characters (a blank or tab; **note**: bad idea to include
          newline in this!).  Use of IS_CHARACTER_JUNK is recommended.
        """

        self.linejunk = linejunk
        self.charjunk = charjunk

    def compare(self, a, b):
        r"""
        Compare two sequences of lines; generate the resulting delta.

        Each sequence must contain individual single-line strings ending with
        newlines. Such sequences can be obtained from the `readlines()` method
        of file-like objects.  The delta generated also consists of newline-
        terminated strings, ready to be printed as-is via the writeline()
        method of a file-like object.

        Example:

        >>> print(''.join(Differ().compare('one\ntwo\nthree\n'.splitlines(1),
        ...                                'ore\ntree\nemu\n'.splitlines(1))),
        ...       end="")
        - one
        ?  ^
        + ore
        ?  ^
        - two
        - three
        ?  -
        + tree
        + emu
        """

        cruncher = SequenceMatcher(self.linejunk, a, b)
        for tag, alo, ahi, blo, bhi in cruncher.get_opcodes():
            if tag == 'replace':
                g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
            elif tag == 'delete':
                g = self._dump('-', a, alo, ahi)
            elif tag == 'insert':
                g = self._dump('+', b, blo, bhi)
            elif tag == 'equal':
                g = self._dump(' ', a, alo, ahi)
            else:
                raise ValueError('unknown tag %r' % (tag,))

            for line in g:
                yield line

    def _dump(self, tag, x, lo, hi):
        """Generate comparison results for a same-tagged range."""
        for i in range(lo, hi):
            yield '%s %s' % (tag, x[i])

    def _plain_replace(self, a, alo, ahi, b, blo, bhi):
        assert alo < ahi and blo < bhi
        # dump the shorter block first -- reduces the burden on short-term
        # memory if the blocks are of very different sizes
        if bhi - blo < ahi - alo:
            first  = self._dump('+', b, blo, bhi)
            second = self._dump('-', a, alo, ahi)
        else:
            first  = self._dump('-', a, alo, ahi)
            second = self._dump('+', b, blo, bhi)

        for g in first, second:
            for line in g:
                yield line

    def _fancy_replace(self, a, alo, ahi, b, blo, bhi):
        r"""
        When replacing one block of lines with another, search the blocks
        for *similar* lines; the best-matching pair (if any) is used as a
        synch point, and intraline difference marking is done on the
        similar pair. Lots of work, but often worth it.

        Example:

        >>> d = Differ()
        >>> results = d._fancy_replace(['abcDefghiJkl\n'], 0, 1,
        ...                            ['abcdefGhijkl\n'], 0, 1)
        >>> print(''.join(results), end="")
        - abcDefghiJkl
        ?    ^  ^  ^
        + abcdefGhijkl
        ?    ^  ^  ^
        """

        # don't synch up unless the lines have a similarity score of at
        # least cutoff; best_ratio tracks the best score seen so far
        best_ratio, cutoff = 0.74, 0.75
        cruncher = SequenceMatcher(self.charjunk)
        eqi, eqj = None, None   # 1st indices of equal lines (if any)

        # search for the pair that matches best without being identical
        # (identical lines must be junk lines, & we don't want to synch up
        # on junk -- unless we have to)
        for j in range(blo, bhi):
            bj = b[j]
            cruncher.set_seq2(bj)
            for i in range(alo, ahi):
                ai = a[i]
                if ai == bj:
                    if eqi is None:
                        eqi, eqj = i, j
                    continue
                cruncher.set_seq1(ai)
                # computing similarity is expensive, so use the quick
                # upper bounds first -- have seen this speed up messy
                # compares by a factor of 3.
                # note that ratio() is only expensive to compute the first
                # time it's called on a sequence pair; the expensive part
                # of the computation is cached by cruncher
                if cruncher.real_quick_ratio() > best_ratio and \
                      cruncher.quick_ratio() > best_ratio and \
                      cruncher.ratio() > best_ratio:
                    best_ratio, best_i, best_j = cruncher.ratio(), i, j
        if best_ratio < cutoff:
            # no non-identical "pretty close" pair
            if eqi is None:
                # no identical pair either -- treat it as a straight replace
                for line in self._plain_replace(a, alo, ahi, b, blo, bhi):
                    yield line
                return
            # no close pair, but an identical pair -- synch up on that
            best_i, best_j, best_ratio = eqi, eqj, 1.0
        else:
            # there's a close pair, so forget the identical pair (if any)
            eqi = None

        # a[best_i] very similar to b[best_j]; eqi is None iff they're not
        # identical

        # pump out diffs from before the synch point
        for line in self._fancy_helper(a, alo, best_i, b, blo, best_j):
            yield line

        # do intraline marking on the synch pair
        aelt, belt = a[best_i], b[best_j]
        if eqi is None:
            # pump out a '-', '?', '+', '?' quad for the synched lines
            atags = btags = ""
            cruncher.set_seqs(aelt, belt)
            for tag, ai1, ai2, bj1, bj2 in cruncher.get_opcodes():
                la, lb = ai2 - ai1, bj2 - bj1
                if tag == 'replace':
                    atags += '^' * la
                    btags += '^' * lb
                elif tag == 'delete':
                    atags += '-' * la
                elif tag == 'insert':
                    btags += '+' * lb
                elif tag == 'equal':
                    atags += ' ' * la
                    btags += ' ' * lb
                else:
                    raise ValueError('unknown tag %r' % (tag,))
            for line in self._qformat(aelt, belt, atags, btags):
                yield line
        else:
            # the synch pair is identical
            yield '  ' + aelt

        # pump out diffs from after the synch point
        for line in self._fancy_helper(a, best_i+1, ahi, b, best_j+1, bhi):
            yield line

    def _fancy_helper(self, a, alo, ahi, b, blo, bhi):
        g = []
        if alo < ahi:
            if blo < bhi:
                g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
            else:
                g = self._dump('-', a, alo, ahi)
        elif blo < bhi:
            g = self._dump('+', b, blo, bhi)

        for line in g:
            yield line

    def _qformat(self, aline, bline, atags, btags):
        r"""
        Format "?" output and deal with leading tabs.

        Example:

        >>> d = Differ()
        >>> results = d._qformat('\tabcDefghiJkl\n', '\tabcdefGhijkl\n',
        ...                      '  ^ ^  ^      ', '  ^ ^  ^      ')
        >>> for line in results: print(repr(line))
        ...
        '- \tabcDefghiJkl\n'
        '? \t ^ ^  ^\n'
        '+ \tabcdefGhijkl\n'
        '? \t ^ ^  ^\n'
        """

        # Can hurt, but will probably help most of the time.
        common = min(_count_leading(aline, "\t"),
                     _count_leading(bline, "\t"))
        common = min(common, _count_leading(atags[:common], " "))
        common = min(common, _count_leading(btags[:common], " "))
        atags = atags[common:].rstrip()
        btags = btags[common:].rstrip()

        yield "- " + aline
        if atags:
            yield "? %s%s\n" % ("\t" * common, atags)

        yield "+ " + bline
        if btags:
            yield "? %s%s\n" % ("\t" * common, btags)

# With respect to junk, an earlier version of ndiff simply refused to
# *start* a match with a junk element.  The result was cases like this:
#     before: private Thread currentThread;
#     after:  private volatile Thread currentThread;
# If you consider whitespace to be junk, the longest contiguous match
# not starting with junk is "e Thread currentThread".  So ndiff reported
# that "e volatil" was inserted between the 't' and the 'e' in "private".
# While an accurate view, to people that's absurd.  The current version
# looks for matching blocks that are entirely junk-free, then extends the
# longest one of those as far as possible but only with matching junk.
# So now "currentThread" is matched, then extended to suck up the
# preceding blank; then "private" is matched, and extended to suck up the
# following blank; then "Thread" is matched; and finally ndiff reports
# that "volatile " was inserted before "Thread".  The only quibble
# remaining is that perhaps it was really the case that " volatile"
# was inserted after "private".  I can live with that <wink>.

import re

def IS_LINE_JUNK(line, pat=re.compile(r"\s*#?\s*$").match):
    r"""
    Return 1 for ignorable line: iff `line` is blank or contains a single '#'.

    Examples:

    >>> IS_LINE_JUNK('\n')
    True
    >>> IS_LINE_JUNK('  #   \n')
    True
    >>> IS_LINE_JUNK('hello\n')
    False
    """

    return pat(line) is not None

def IS_CHARACTER_JUNK(ch, ws=" \t"):
    r"""
    Return 1 for ignorable character: iff `ch` is a space or tab.

    Examples:

    >>> IS_CHARACTER_JUNK(' ')
    True
    >>> IS_CHARACTER_JUNK('\t')
    True
    >>> IS_CHARACTER_JUNK('\n')
    False
    >>> IS_CHARACTER_JUNK('x')
    False
    """

    return ch in ws


########################################################################
###  Unified Diff
########################################################################

def _format_range_unified(start, stop):
    'Convert range to the "ed" format'
    # Per the diff spec at http://www.unix.org/single_unix_specification/
    beginning = start + 1     # lines start numbering with one
    length = stop - start
    if length == 1:
        return '{}'.format(beginning)
    if not length:
        beginning -= 1        # empty ranges begin at line just before the range
    return '{},{}'.format(beginning, length)

def unified_diff(a, b, fromfile='', tofile='', fromfiledate='',
                 tofiledate='', n=3, lineterm='\n'):
    r"""
    Compare two sequences of lines; generate the delta as a unified diff.

    Unified diffs are a compact way of showing line changes and a few
    lines of context.  The number of context lines is set by 'n' which
    defaults to three.

    By default, the diff control lines (those with ---, +++, or @@) are
    created with a trailing newline.  This is helpful so that inputs
    created from file.readlines() result in diffs that are suitable for
    file.writelines() since both the inputs and outputs have trailing
    newlines.

    For inputs that do not have trailing newlines, set the lineterm
    argument to "" so that the output will be uniformly newline free.

    The unidiff format normally has a header for filenames and modification
    times.  Any or all of these may be specified using strings for
    'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
    The modification times are normally expressed in the ISO 8601 format.

    Example:

    >>> for line in unified_diff('one two three four'.split(),
    ...             'zero one tree four'.split(), 'Original', 'Current',
    ...             '2005-01-26 23:30:50', '2010-04-02 10:20:52',
    ...             lineterm=''):
    ...     print(line)                 # doctest: +NORMALIZE_WHITESPACE
    --- Original        2005-01-26 23:30:50
    +++ Current         2010-04-02 10:20:52
    @@ -1,4 +1,4 @@
    +zero
     one
    -two
    -three
    +tree
     four
    """

    started = False
    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
        if not started:
            started = True
            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else ''
            todate = '\t{}'.format(tofiledate) if tofiledate else ''
            yield '--- {}{}{}'.format(fromfile, fromdate, lineterm)
            yield '+++ {}{}{}'.format(tofile, todate, lineterm)

        first, last = group[0], group[-1]
        file1_range = _format_range_unified(first[1], last[2])
        file2_range = _format_range_unified(first[3], last[4])
        yield '@@ -{} +{} @@{}'.format(file1_range, file2_range, lineterm)

        for tag, i1, i2, j1, j2 in group:
            if tag == 'equal':
                for line in a[i1:i2]:
                    yield ' ' + line
                continue
            if tag in {'replace', 'delete'}:
                for line in a[i1:i2]:
                    yield '-' + line
            if tag in {'replace', 'insert'}:
                for line in b[j1:j2]:
                    yield '+' + line


########################################################################
###  Context Diff
########################################################################

def _format_range_context(start, stop):
    'Convert range to the "ed" format'
    # Per the diff spec at http://www.unix.org/single_unix_specification/
    beginning = start + 1     # lines start numbering with one
    length = stop - start
    if not length:
        beginning -= 1        # empty ranges begin at line just before the range
    if length <= 1:
        return '{}'.format(beginning)
    return '{},{}'.format(beginning, beginning + length - 1)

# See http://www.unix.org/single_unix_specification/
def context_diff(a, b, fromfile='', tofile='',
                 fromfiledate='', tofiledate='', n=3, lineterm='\n'):
    r"""
    Compare two sequences of lines; generate the delta as a context diff.

    Context diffs are a compact way of showing line changes and a few
    lines of context.  The number of context lines is set by 'n' which
    defaults to three.

    By default, the diff control lines (those with *** or ---) are
    created with a trailing newline.  This is helpful so that inputs
    created from file.readlines() result in diffs that are suitable for
    file.writelines() since both the inputs and outputs have trailing
    newlines.

    For inputs that do not have trailing newlines, set the lineterm
    argument to "" so that the output will be uniformly newline free.

    The context diff format normally has a header for filenames and
    modification times.  Any or all of these may be specified using
    strings for 'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.
    The modification times are normally expressed in the ISO 8601 format.
    If not specified, the strings default to blanks.

    Example:

    >>> print(''.join(context_diff('one\ntwo\nthree\nfour\n'.splitlines(1),
    ...       'zero\none\ntree\nfour\n'.splitlines(1), 'Original', 'Current')),
    ...       end="")
    *** Original
    --- Current
    ***************
    *** 1,4 ****
      one
    ! two
    ! three
      four
    --- 1,4 ----
    + zero
      one
    ! tree
      four
    """

    prefix = dict(insert='+ ', delete='- ', replace='! ', equal='  ')
    started = False
    for group in SequenceMatcher(None,a,b).get_grouped_opcodes(n):
        if not started:
            started = True
            fromdate = '\t{}'.format(fromfiledate) if fromfiledate else ''
            todate = '\t{}'.format(tofiledate) if tofiledate else ''
            yield '*** {}{}{}'.format(fromfile, fromdate, lineterm)
            yield '--- {}{}{}'.format(tofile, todate, lineterm)

        first, last = group[0], group[-1]
        yield '***************' + lineterm

        file1_range = _format_range_context(first[1], last[2])
        yield '*** {} ****{}'.format(file1_range, lineterm)

        if any(tag in {'replace', 'delete'} for tag, _, _, _, _ in group):
            for tag, i1, i2, _, _ in group:
                if tag != 'insert':
                    for line in a[i1:i2]:
                        yield prefix[tag] + line

        file2_range = _format_range_context(first[3], last[4])
        yield '--- {} ----{}'.format(file2_range, lineterm)

        if any(tag in {'replace', 'insert'} for tag, _, _, _, _ in group):
            for tag, _, _, j1, j2 in group:
                if tag != 'delete':
                    for line in b[j1:j2]:
                        yield prefix[tag] + line

def ndiff(a, b, linejunk=None, charjunk=IS_CHARACTER_JUNK):
    r"""
    Compare `a` and `b` (lists of strings); return a `Differ`-style delta.

    Optional keyword parameters `linejunk` and `charjunk` are for filter
    functions (or None):

    - linejunk: A function that should accept a single string argument, and
      return true iff the string is junk.  The default is None, and is
      recommended; as of Python 2.3, an adaptive notion of "noise" lines is
      used that does a good job on its own.

    - charjunk: A function that should accept a string of length 1. The
      default is module-level function IS_CHARACTER_JUNK, which filters out
      whitespace characters (a blank or tab; note: bad idea to include newline
      in this!).

    Tools/scripts/ndiff.py is a command-line front-end to this function.

    Example:

    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
    ...              'ore\ntree\nemu\n'.splitlines(1))
    >>> print(''.join(diff), end="")
    - one
    ?  ^
    + ore
    ?  ^
    - two
    - three
    ?  -
    + tree
    + emu
    """
    return Differ(linejunk, charjunk).compare(a, b)

def _mdiff(fromlines, tolines, context=None, linejunk=None,
           charjunk=IS_CHARACTER_JUNK):
    r"""Returns generator yielding marked up from/to side by side differences.

    Arguments:
    fromlines -- list of text lines to compared to tolines
    tolines -- list of text lines to be compared to fromlines
    context -- number of context lines to display on each side of difference,
               if None, all from/to text lines will be generated.
    linejunk -- passed on to ndiff (see ndiff documentation)
    charjunk -- passed on to ndiff (see ndiff documentation)

    This function returns an interator which returns a tuple:
    (from line tuple, to line tuple, boolean flag)

    from/to line tuple -- (line num, line text)
        line num -- integer or None (to indicate a context separation)
        line text -- original line text with following markers inserted:
            '\0+' -- marks start of added text
            '\0-' -- marks start of deleted text
            '\0^' -- marks start of changed text
            '\1' -- marks end of added/deleted/changed text

    boolean flag -- None indicates context separation, True indicates
        either "from" or "to" line contains a change, otherwise False.

    This function/iterator was originally developed to generate side by side
    file difference for making HTML pages (see HtmlDiff class for example
    usage).

    Note, this function utilizes the ndiff function to generate the side by
    side difference markup.  Optional ndiff arguments may be passed to this
    function and they in turn will be passed to ndiff.
    """
    import re

    # regular expression for finding intraline change indices
    change_re = re.compile('(\++|\-+|\^+)')

    # create the difference iterator to generate the differences
    diff_lines_iterator = ndiff(fromlines,tolines,linejunk,charjunk)

    def _make_line(lines, format_key, side, num_lines=[0,0]):
        """Returns line of text with user's change markup and line formatting.

        lines -- list of lines from the ndiff generator to produce a line of
                 text from.  When producing the line of text to return, the
                 lines used are removed from this list.
        format_key -- '+' return first line in list with "add" markup around
                          the entire line.
                      '-' return first line in list with "delete" markup around
                          the entire line.
                      '?' return first line in list with add/delete/change
                          intraline markup (indices obtained from second line)
                      None return first line in list with no markup
        side -- indice into the num_lines list (0=from,1=to)
        num_lines -- from/to current line number.  This is NOT intended to be a
                     passed parameter.  It is present as a keyword argument to
                     maintain memory of the current line numbers between calls
                     of this function.

        Note, this function is purposefully not defined at the module scope so
        that data it needs from its parent function (within whose context it
        is defined) does not need to be of module scope.
        """
        num_lines[side] += 1
        # Handle case where no user markup is to be added, just return line of
        # text with user's line format to allow for usage of the line number.
        if format_key is None:
            return (num_lines[side],lines.pop(0)[2:])
        # Handle case of intraline changes
        if format_key == '?':
            text, markers = lines.pop(0), lines.pop(0)
            # find intraline changes (store change type and indices in tuples)
            sub_info = []
            def record_sub_info(match_object,sub_info=sub_info):
                sub_info.append([match_object.group(1)[0],match_object.span()])
                return match_object.group(1)
            change_re.sub(record_sub_info,markers)
            # process each tuple inserting our special marks that won't be
            # noticed by an xml/html escaper.
            for key,(begin,end) in sub_info[::-1]:
                text = text[0:begin]+'\0'+key+text[begin:end]+'\1'+text[end:]
            text = text[2:]
        # Handle case of add/delete entire line
        else:
            text = lines.pop(0)[2:]
            # if line of text is just a newline, insert a space so there is
            # something for the user to highlight and see.
            if not text:
                text = ' '
            # insert marks that won't be noticed by an xml/html escaper.
            text = '\0' + format_key + text + '\1'
        # Return line of text, first allow user's line formatter to do its
        # thing (such as adding the line number) then replace the special
        # marks with what the user's change markup.
        return (num_lines[side],text)

    def _line_iterator():
        """Yields from/to lines of text with a change indication.

        This function is an iterator.  It itself pulls lines from a
        differencing iterator, processes them and yields them.  When it can
        it yields both a "from" and a "to" line, otherwise it will yield one
        or the other.  In addition to yielding the lines of from/to text, a
        boolean flag is yielded to indicate if the text line(s) have
        differences in them.

        Note, this function is purposefully not defined at the module scope so
        that data it needs from its parent function (within whose context it
        is defined) does not need to be of module scope.
        """
        lines = []
        num_blanks_pending, num_blanks_to_yield = 0, 0
        while True:
            # Load up next 4 lines so we can look ahead, create strings which
            # are a concatenation of the first character of each of the 4 lines
            # so we can do some very readable comparisons.
            while len(lines) < 4:
                try:
                    lines.append(next(diff_lines_iterator))
                except StopIteration:
                    lines.append('X')
            s = ''.join([line[0] for line in lines])
            if s.startswith('X'):
                # When no more lines, pump out any remaining blank lines so the
                # corresponding add/delete lines get a matching blank line so
                # all line pairs get yielded at the next level.
                num_blanks_to_yield = num_blanks_pending
            elif s.startswith('-?+?'):
                # simple intraline change
                yield _make_line(lines,'?',0), _make_line(lines,'?',1), True
                continue
            elif s.startswith('--++'):
                # in delete block, add block coming: we do NOT want to get
                # caught up on blank lines yet, just process the delete line
                num_blanks_pending -= 1
                yield _make_line(lines,'-',0), None, True
                continue
            elif s.startswith(('--?+', '--+', '- ')):
                # in delete block and see a intraline change or unchanged line
                # coming: yield the delete line and then blanks
                from_line,to_line = _make_line(lines,'-',0), None
                num_blanks_to_yield,num_blanks_pending = num_blanks_pending-1,0
            elif s.startswith('-+?'):
                # intraline change
                yield _make_line(lines,None,0), _make_line(lines,'?',1), True
                continue
            elif s.startswith('-?+'):
                # intraline change
                yield _make_line(lines,'?',0), _make_line(lines,None,1), True
                continue
            elif s.startswith('-'):
                # delete FROM line
                num_blanks_pending -= 1
                yield _make_line(lines,'-',0), None, True
                continue
            elif s.startswith('+--'):
                # in add block, delete block coming: we do NOT want to get
                # caught up on blank lines yet, just process the add line
                num_blanks_pending += 1
                yield None, _make_line(lines,'+',1), True
                continue
            elif s.startswith(('+ ', '+-')):
                # will be leaving an add block: yield blanks then add line
                from_line, to_line = None, _make_line(lines,'+',1)
                num_blanks_to_yield,num_blanks_pending = num_blanks_pending+1,0
            elif s.startswith('+'):
                # inside an add block, yield the add line
                num_blanks_pending += 1
                yield None, _make_line(lines,'+',1), True
                continue
            elif s.startswith(' '):
                # unchanged text, yield it to both sides
                yield _make_line(lines[:],None,0),_make_line(lines,None,1),False
                continue
            # Catch up on the blank lines so when we yield the next from/to
            # pair, they are lined up.
            while(num_blanks_to_yield < 0):
                num_blanks_to_yield += 1
                yield None,('','\n'),True
            while(num_blanks_to_yield > 0):
                num_blanks_to_yield -= 1
                yield ('','\n'),None,True
            if s.startswith('X'):
                raise StopIteration
            else:
                yield from_line,to_line,True

    def _line_pair_iterator():
        """Yields from/to lines of text with a change indication.

        This function is an iterator.  It itself pulls lines from the line
        iterator.  Its difference from that iterator is that this function
        always yields a pair of from/to text lines (with the change
        indication).  If necessary it will collect single from/to lines
        until it has a matching pair from/to pair to yield.

        Note, this function is purposefully not defined at the module scope so
        that data it needs from its parent function (within whose context it
        is defined) does not need to be of module scope.
        """
        line_iterator = _line_iterator()
        fromlines,tolines=[],[]
        while True:
            # Collecting lines of text until we have a from/to pair
            while (len(fromlines)==0 or len(tolines)==0):
                from_line, to_line, found_diff = next(line_iterator)
                if from_line is not None:
                    fromlines.append((from_line,found_diff))
                if to_line is not None:
                    tolines.append((to_line,found_diff))
            # Once we have a pair, remove them from the collection and yield it
            from_line, fromDiff = fromlines.pop(0)
            to_line, to_diff = tolines.pop(0)
            yield (from_line,to_line,fromDiff or to_diff)

    # Handle case where user does not want context differencing, just yield
    # them up without doing anything else with them.
    line_pair_iterator = _line_pair_iterator()
    if context is None:
        while True:
            yield next(line_pair_iterator)
    # Handle case where user wants context differencing.  We must do some
    # storage of lines until we know for sure that they are to be yielded.
    else:
        context += 1
        lines_to_write = 0
        while True:
            # Store lines up until we find a difference, note use of a
            # circular queue because we only need to keep around what
            # we need for context.
            index, contextLines = 0, [None]*(context)
            found_diff = False
            while(found_diff is False):
                from_line, to_line, found_diff = next(line_pair_iterator)
                i = index % context
                contextLines[i] = (from_line, to_line, found_diff)
                index += 1
            # Yield lines that we have collected so far, but first yield
            # the user's separator.
            if index > context:
                yield None, None, None
                lines_to_write = context
            else:
                lines_to_write = index
                index = 0
            while(lines_to_write):
                i = index % context
                index += 1
                yield contextLines[i]
                lines_to_write -= 1
            # Now yield the context lines after the change
            lines_to_write = context-1
            while(lines_to_write):
                from_line, to_line, found_diff = next(line_pair_iterator)
                # If another change within the context, extend the context
                if found_diff:
                    lines_to_write = context-1
                else:
                    lines_to_write -= 1
                yield from_line, to_line, found_diff


_file_template = """
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html>

<head>
    <meta http-equiv="Content-Type"
          content="text/html; charset=ISO-8859-1" />
    <title></title>
    <style type="text/css">%(styles)s
    </style>
</head>

<body>
    %(table)s%(legend)s
</body>

</html>"""

_styles = """
        table.diff {font-family:Courier; border:medium;}
        .diff_header {background-color:#e0e0e0}
        td.diff_header {text-align:right}
        .diff_next {background-color:#c0c0c0}
        .diff_add {background-color:#aaffaa}
        .diff_chg {background-color:#ffff77}
        .diff_sub {background-color:#ffaaaa}"""

_table_template = """
    <table class="diff" id="difflib_chg_%(prefix)s_top"
           cellspacing="0" cellpadding="0" rules="groups" >
        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
        <colgroup></colgroup> <colgroup></colgroup> <colgroup></colgroup>
        %(header_row)s
        <tbody>
%(data_rows)s        </tbody>
    </table>"""

_legend = """
    <table class="diff" summary="Legends">
        <tr> <th colspan="2"> Legends </th> </tr>
        <tr> <td> <table border="" summary="Colors">
                      <tr><th> Colors </th> </tr>
                      <tr><td class="diff_add">&nbsp;Added&nbsp;</td></tr>
                      <tr><td class="diff_chg">Changed</td> </tr>
                      <tr><td class="diff_sub">Deleted</td> </tr>
                  </table></td>
             <td> <table border="" summary="Links">
                      <tr><th colspan="2"> Links </th> </tr>
                      <tr><td>(f)irst change</td> </tr>
                      <tr><td>(n)ext change</td> </tr>
                      <tr><td>(t)op</td> </tr>
                  </table></td> </tr>
    </table>"""

class HtmlDiff(object):
    """For producing HTML side by side comparison with change highlights.

    This class can be used to create an HTML table (or a complete HTML file
    containing the table) showing a side by side, line by line comparison
    of text with inter-line and intra-line change highlights.  The table can
    be generated in either full or contextual difference mode.

    The following methods are provided for HTML generation:

    make_table -- generates HTML for a single side by side table
    make_file -- generates complete HTML file with a single side by side table

    See tools/scripts/diff.py for an example usage of this class.
    """

    _file_template = _file_template
    _styles = _styles
    _table_template = _table_template
    _legend = _legend
    _default_prefix = 0

    def __init__(self,tabsize=8,wrapcolumn=None,linejunk=None,
                 charjunk=IS_CHARACTER_JUNK):
        """HtmlDiff instance initializer

        Arguments:
        tabsize -- tab stop spacing, defaults to 8.
        wrapcolumn -- column number where lines are broken and wrapped,
            defaults to None where lines are not wrapped.
        linejunk,charjunk -- keyword arguments passed into ndiff() (used to by
            HtmlDiff() to generate the side by side HTML differences).  See
            ndiff() documentation for argument default values and descriptions.
        """
        self._tabsize = tabsize
        self._wrapcolumn = wrapcolumn
        self._linejunk = linejunk
        self._charjunk = charjunk

    def make_file(self,fromlines,tolines,fromdesc='',todesc='',context=False,
                  numlines=5):
        """Returns HTML file of side by side comparison with change highlights

        Arguments:
        fromlines -- list of "from" lines
        tolines -- list of "to" lines
        fromdesc -- "from" file column header string
        todesc -- "to" file column header string
        context -- set to True for contextual differences (defaults to False
            which shows full differences).
        numlines -- number of context lines.  When context is set True,
            controls number of lines displayed before and after the change.
            When context is False, controls the number of lines to place
            the "next" link anchors before the next change (so click of
            "next" link jumps to just before the change).
        """

        return self._file_template % dict(
            styles = self._styles,
            legend = self._legend,
            table = self.make_table(fromlines,tolines,fromdesc,todesc,
                                    context=context,numlines=numlines))

    def _tab_newline_replace(self,fromlines,tolines):
        """Returns from/to line lists with tabs expanded and newlines removed.

        Instead of tab characters being replaced by the number of spaces
        needed to fill in to the next tab stop, this function will fill
        the space with tab characters.  This is done so that the difference
        algorithms can identify changes in a file when tabs are replaced by
        spaces and vice versa.  At the end of the HTML generation, the tab
        characters will be replaced with a nonbreakable space.
        """
        def expand_tabs(line):
            # hide real spaces
            line = line.replace(' ','\0')
            # expand tabs into spaces
            line = line.expandtabs(self._tabsize)
            # replace spaces from expanded tabs back into tab characters
            # (we'll replace them with markup after we do differencing)
            line = line.replace(' ','\t')
            return line.replace('\0',' ').rstrip('\n')
        fromlines = [expand_tabs(line) for line in fromlines]
        tolines = [expand_tabs(line) for line in tolines]
        return fromlines,tolines

    def _split_line(self,data_list,line_num,text):
        """Builds list of text lines by splitting text lines at wrap point

        This function will determine if the input text line needs to be
        wrapped (split) into separate lines.  If so, the first wrap point
        will be determined and the first line appended to the output
        text line list.  This function is used recursively to handle
        the second part of the split line to further split it.
        """
        # if blank line or context separator, just add it to the output list
        if not line_num:
            data_list.append((line_num,text))
            return

        # if line text doesn't need wrapping, just add it to the output list
        size = len(text)
        max = self._wrapcolumn
        if (size <= max) or ((size -(text.count('\0')*3)) <= max):
            data_list.append((line_num,text))
            return

        # scan text looking for the wrap point, keeping track if the wrap
        # point is inside markers
        i = 0
        n = 0
        mark = ''
        while n < max and i < size:
            if text[i] == '\0':
                i += 1
                mark = text[i]
                i += 1
            elif text[i] == '\1':
                i += 1
                mark = ''
            else:
                i += 1
                n += 1

        # wrap point is inside text, break it up into separate lines
        line1 = text[:i]
        line2 = text[i:]

        # if wrap point is inside markers, place end marker at end of first
        # line and start marker at beginning of second line because each
        # line will have its own table tag markup around it.
        if mark:
            line1 = line1 + '\1'
            line2 = '\0' + mark + line2

        # tack on first line onto the output list
        data_list.append((line_num,line1))

        # use this routine again to wrap the remaining text
        self._split_line(data_list,'>',line2)

    def _line_wrapper(self,diffs):
        """Returns iterator that splits (wraps) mdiff text lines"""

        # pull from/to data and flags from mdiff iterator
        for fromdata,todata,flag in diffs:
            # check for context separators and pass them through
            if flag is None:
                yield fromdata,todata,flag
                continue
            (fromline,fromtext),(toline,totext) = fromdata,todata
            # for each from/to line split it at the wrap column to form
            # list of text lines.
            fromlist,tolist = [],[]
            self._split_line(fromlist,fromline,fromtext)
            self._split_line(tolist,toline,totext)
            # yield from/to line in pairs inserting blank lines as
            # necessary when one side has more wrapped lines
            while fromlist or tolist:
                if fromlist:
                    fromdata = fromlist.pop(0)
                else:
                    fromdata = ('',' ')
                if tolist:
                    todata = tolist.pop(0)
                else:
                    todata = ('',' ')
                yield fromdata,todata,flag

    def _collect_lines(self,diffs):
        """Collects mdiff output into separate lists

        Before storing the mdiff from/to data into a list, it is converted
        into a single line of text with HTML markup.
        """

        fromlist,tolist,flaglist = [],[],[]
        # pull from/to data and flags from mdiff style iterator
        for fromdata,todata,flag in diffs:
            try:
                # store HTML markup of the lines into the lists
                fromlist.append(self._format_line(0,flag,*fromdata))
                tolist.append(self._format_line(1,flag,*todata))
            except TypeError:
                # exceptions occur for lines where context separators go
                fromlist.append(None)
                tolist.append(None)
            flaglist.append(flag)
        return fromlist,tolist,flaglist

    def _format_line(self,side,flag,linenum,text):
        """Returns HTML markup of "from" / "to" text lines

        side -- 0 or 1 indicating "from" or "to" text
        flag -- indicates if difference on line
        linenum -- line number (used for line number column)
        text -- line text to be marked up
        """
        try:
            linenum = '%d' % linenum
            id = ' id="%s%s"' % (self._prefix[side],linenum)
        except TypeError:
            # handle blank lines where linenum is '>' or ''
            id = ''
        # replace those things that would get confused with HTML symbols
        text=text.replace("&","&amp;").replace(">","&gt;").replace("<","&lt;")

        # make space non-breakable so they don't get compressed or line wrapped
        text = text.replace(' ','&nbsp;').rstrip()

        return '<td class="diff_header"%s>%s</td><td nowrap="nowrap">%s</td>' \
               % (id,linenum,text)

    def _make_prefix(self):
        """Create unique anchor prefixes"""

        # Generate a unique anchor prefix so multiple tables
        # can exist on the same HTML page without conflicts.
        fromprefix = "from%d_" % HtmlDiff._default_prefix
        toprefix = "to%d_" % HtmlDiff._default_prefix
        HtmlDiff._default_prefix += 1
        # store prefixes so line format method has access
        self._prefix = [fromprefix,toprefix]

    def _convert_flags(self,fromlist,tolist,flaglist,context,numlines):
        """Makes list of "next" links"""

        # all anchor names will be generated using the unique "to" prefix
        toprefix = self._prefix[1]

        # process change flags, generating middle column of next anchors/links
        next_id = ['']*len(flaglist)
        next_href = ['']*len(flaglist)
        num_chg, in_change = 0, False
        last = 0
        for i,flag in enumerate(flaglist):
            if flag:
                if not in_change:
                    in_change = True
                    last = i
                    # at the beginning of a change, drop an anchor a few lines
                    # (the context lines) before the change for the previous
                    # link
                    i = max([0,i-numlines])
                    next_id[i] = ' id="difflib_chg_%s_%d"' % (toprefix,num_chg)
                    # at the beginning of a change, drop a link to the next
                    # change
                    num_chg += 1
                    next_href[last] = '<a href="#difflib_chg_%s_%d">n</a>' % (
                         toprefix,num_chg)
            else:
                in_change = False
        # check for cases where there is no content to avoid exceptions
        if not flaglist:
            flaglist = [False]
            next_id = ['']
            next_href = ['']
            last = 0
            if context:
                fromlist = ['<td></td><td>&nbsp;No Differences Found&nbsp;</td>']
                tolist = fromlist
            else:
                fromlist = tolist = ['<td></td><td>&nbsp;Empty File&nbsp;</td>']
        # if not a change on first line, drop a link
        if not flaglist[0]:
            next_href[0] = '<a href="#difflib_chg_%s_0">f</a>' % toprefix
        # redo the last link to link to the top
        next_href[last] = '<a href="#difflib_chg_%s_top">t</a>' % (toprefix)

        return fromlist,tolist,flaglist,next_href,next_id

    def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False,
                   numlines=5):
        """Returns HTML table of side by side comparison with change highlights

        Arguments:
        fromlines -- list of "from" lines
        tolines -- list of "to" lines
        fromdesc -- "from" file column header string
        todesc -- "to" file column header string
        context -- set to True for contextual differences (defaults to False
            which shows full differences).
        numlines -- number of context lines.  When context is set True,
            controls number of lines displayed before and after the change.
            When context is False, controls the number of lines to place
            the "next" link anchors before the next change (so click of
            "next" link jumps to just before the change).
        """

        # make unique anchor prefixes so that multiple tables may exist
        # on the same page without conflict.
        self._make_prefix()

        # change tabs to spaces before it gets more difficult after we insert
        # markkup
        fromlines,tolines = self._tab_newline_replace(fromlines,tolines)

        # create diffs iterator which generates side by side from/to data
        if context:
            context_lines = numlines
        else:
            context_lines = None
        diffs = _mdiff(fromlines,tolines,context_lines,linejunk=self._linejunk,
                      charjunk=self._charjunk)

        # set up iterator to wrap lines that exceed desired width
        if self._wrapcolumn:
            diffs = self._line_wrapper(diffs)

        # collect up from/to lines and flags into lists (also format the lines)
        fromlist,tolist,flaglist = self._collect_lines(diffs)

        # process change flags, generating middle column of next anchors/links
        fromlist,tolist,flaglist,next_href,next_id = self._convert_flags(
            fromlist,tolist,flaglist,context,numlines)

        s = []
        fmt = '            <tr><td class="diff_next"%s>%s</td>%s' + \
              '<td class="diff_next">%s</td>%s</tr>\n'
        for i in range(len(flaglist)):
            if flaglist[i] is None:
                # mdiff yields None on separator lines skip the bogus ones
                # generated for the first line
                if i > 0:
                    s.append('        </tbody>        \n        <tbody>\n')
            else:
                s.append( fmt % (next_id[i],next_href[i],fromlist[i],
                                           next_href[i],tolist[i]))
        if fromdesc or todesc:
            header_row = '<thead><tr>%s%s%s%s</tr></thead>' % (
                '<th class="diff_next"><br /></th>',
                '<th colspan="2" class="diff_header">%s</th>' % fromdesc,
                '<th class="diff_next"><br /></th>',
                '<th colspan="2" class="diff_header">%s</th>' % todesc)
        else:
            header_row = ''

        table = self._table_template % dict(
            data_rows=''.join(s),
            header_row=header_row,
            prefix=self._prefix[1])

        return table.replace('\0+','<span class="diff_add">'). \
                     replace('\0-','<span class="diff_sub">'). \
                     replace('\0^','<span class="diff_chg">'). \
                     replace('\1','</span>'). \
                     replace('\t','&nbsp;')

del re

def restore(delta, which):
    r"""
    Generate one of the two sequences that generated a delta.

    Given a `delta` produced by `Differ.compare()` or `ndiff()`, extract
    lines originating from file 1 or 2 (parameter `which`), stripping off line
    prefixes.

    Examples:

    >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
    ...              'ore\ntree\nemu\n'.splitlines(1))
    >>> diff = list(diff)
    >>> print(''.join(restore(diff, 1)), end="")
    one
    two
    three
    >>> print(''.join(restore(diff, 2)), end="")
    ore
    tree
    emu
    """
    try:
        tag = {1: "- ", 2: "+ "}[int(which)]
    except KeyError:
        raise ValueError('unknown delta choice (must be 1 or 2): %r'
                           % which)
    prefixes = ("  ", tag)
    for line in delta:
        if line[:2] in prefixes:
            yield line[2:]

def _test():
    import doctest, difflib
    return doctest.testmod(difflib)

if __name__ == "__main__":
    _test()
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.