Source

pypy / pypy / module / itertools / interp_itertools.py

Full commit
   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
from pypy.interpreter.baseobjspace import Wrappable
from pypy.interpreter.error import OperationError
from pypy.interpreter.typedef import TypeDef, make_weakref_descr
from pypy.interpreter.gateway import interp2app, unwrap_spec

class W_Count(Wrappable):

    def __init__(self, space, w_firstval, w_step):
        self.space = space
        self.w_c = w_firstval
        self.w_step = w_step

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        w_c = self.w_c
        self.w_c = self.space.add(w_c, self.w_step)
        return w_c

    def single_argument(self):
        space = self.space
        return (space.isinstance_w(self.w_step, space.w_int) and
                space.eq_w(self.w_step, space.wrap(1)))

    def repr_w(self):
        space = self.space
        c = space.str_w(space.repr(self.w_c))
        if self.single_argument():
            s = 'count(%s)' % (c,)
        else:
            step = space.str_w(space.repr(self.w_step))
            s = 'count(%s, %s)' % (c, step)
        return self.space.wrap(s)

    def reduce_w(self):
        space = self.space
        if self.single_argument():
            args_w = [self.w_c]
        else:
            args_w = [self.w_c, self.w_step]
        return space.newtuple([space.gettypefor(W_Count),
                               space.newtuple(args_w)])

def check_number(space, w_obj):
    if (space.lookup(w_obj, '__add__') is None or
        space.is_true(space.isinstance(w_obj, space.w_str)) or
        space.is_true(space.isinstance(w_obj, space.w_unicode))):
        raise OperationError(space.w_TypeError,
                             space.wrap("expected a number"))

def W_Count___new__(space, w_subtype, w_start=0, w_step=1):
    check_number(space, w_start)
    check_number(space, w_step)
    r = space.allocate_instance(W_Count, w_subtype)
    r.__init__(space, w_start, w_step)
    return space.wrap(r)

W_Count.typedef = TypeDef(
        'count',
        __module__ = 'itertools',
        __new__ = interp2app(W_Count___new__),
        __iter__ = interp2app(W_Count.iter_w),
        next = interp2app(W_Count.next_w),
        __reduce__ = interp2app(W_Count.reduce_w),
        __repr__ = interp2app(W_Count.repr_w),
        __doc__ = """Make an iterator that returns consecutive integers starting
    with n.  If not specified n defaults to zero. Does not currently
    support python long integers. Often used as an argument to imap()
    to generate consecutive data points.  Also, used with izip() to
    add sequence numbers.

    Equivalent to :

    def count(n=0):
        if not isinstance(n, int):
            raise TypeError("%s is not a regular integer" % n)
        while True:
            yield n
            n += 1
    """)


class W_Repeat(Wrappable):

    def __init__(self, space, w_obj, w_times):
        self.space = space
        self.w_obj = w_obj

        if space.is_w(w_times, space.w_None):
            self.counting = False
            self.count = 0
        else:
            self.counting = True
            self.count = self.space.int_w(w_times)

    def next_w(self):
        if self.counting:
            if self.count <= 0:
                raise OperationError(self.space.w_StopIteration, self.space.w_None)
            self.count -= 1
        return self.w_obj

    def iter_w(self):
        return self.space.wrap(self)

    def repr_w(self):
        objrepr = self.space.str_w(self.space.repr(self.w_obj))
        if self.counting:
            s = 'repeat(%s, %d)' % (objrepr, self.count)
        else:
            s = 'repeat(%s)' % (objrepr,)
        return self.space.wrap(s)

def W_Repeat___new__(space, w_subtype, w_object, w_times=None):
    r = space.allocate_instance(W_Repeat, w_subtype)
    r.__init__(space, w_object, w_times)
    return space.wrap(r)

W_Repeat.typedef = TypeDef(
        'repeat',
        __module__ = 'itertools',
        __new__  = interp2app(W_Repeat___new__),
        __iter__ = interp2app(W_Repeat.iter_w),
        next     = interp2app(W_Repeat.next_w),
        __repr__ = interp2app(W_Repeat.repr_w),
        __doc__  = """Make an iterator that returns object over and over again.
    Runs indefinitely unless the times argument is specified.  Used
    as argument to imap() for invariant parameters to the called
    function. Also used with izip() to create an invariant part of a
    tuple record.

    Equivalent to :

    def repeat(object, times=None):
        if times is None:
            while True:
                yield object
        else:
            for i in xrange(times):
                yield object
    """)

class W_TakeWhile(Wrappable):

    def __init__(self, space, w_predicate, w_iterable):
        self.space = space
        self.w_predicate = w_predicate
        self.iterable = space.iter(w_iterable)
        self.stopped = False

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        if self.stopped:
            raise OperationError(self.space.w_StopIteration, self.space.w_None)

        w_obj = self.space.next(self.iterable)  # may raise a w_StopIteration
        w_bool = self.space.call_function(self.w_predicate, w_obj)
        if not self.space.is_true(w_bool):
            self.stopped = True
            raise OperationError(self.space.w_StopIteration, self.space.w_None)

        return w_obj

def W_TakeWhile___new__(space, w_subtype, w_predicate, w_iterable):
    r = space.allocate_instance(W_TakeWhile, w_subtype)
    r.__init__(space, w_predicate, w_iterable)
    return space.wrap(r)


W_TakeWhile.typedef = TypeDef(
        'takewhile',
        __module__ = 'itertools',
        __new__  = interp2app(W_TakeWhile___new__),
        __iter__ = interp2app(W_TakeWhile.iter_w),
        next     = interp2app(W_TakeWhile.next_w),
        __doc__  = """Make an iterator that returns elements from the iterable as
    long as the predicate is true.

    Equivalent to :

    def takewhile(predicate, iterable):
        for x in iterable:
            if predicate(x):
                yield x
            else:
                break
    """)

class W_DropWhile(Wrappable):

    def __init__(self, space, w_predicate, w_iterable):
        self.space = space
        self.w_predicate = w_predicate
        self.iterable = space.iter(w_iterable)
        self.started = False

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        if self.started:
            w_obj = self.space.next(self.iterable)  # may raise w_StopIteration
        else:
            while True:
                w_obj = self.space.next(self.iterable)  # may raise w_StopIter
                w_bool = self.space.call_function(self.w_predicate, w_obj)
                if not self.space.is_true(w_bool):
                    self.started = True
                    break

        return w_obj

def W_DropWhile___new__(space, w_subtype, w_predicate, w_iterable):
    r = space.allocate_instance(W_DropWhile, w_subtype)
    r.__init__(space, w_predicate, w_iterable)
    return space.wrap(r)


W_DropWhile.typedef = TypeDef(
        'dropwhile',
        __module__ = 'itertools',
        __new__  = interp2app(W_DropWhile___new__),
        __iter__ = interp2app(W_DropWhile.iter_w),
        next     = interp2app(W_DropWhile.next_w),
        __doc__  = """Make an iterator that drops elements from the iterable as long
    as the predicate is true; afterwards, returns every
    element. Note, the iterator does not produce any output until the
    predicate is true, so it may have a lengthy start-up time.

    Equivalent to :

    def dropwhile(predicate, iterable):
        iterable = iter(iterable)
        for x in iterable:
            if not predicate(x):
                yield x
                break
        for x in iterable:
            yield x
    """)

class _IFilterBase(Wrappable):

    def __init__(self, space, w_predicate, w_iterable):
        self.space = space
        if space.is_w(w_predicate, space.w_None):
            self.no_predicate = True
        else:
            self.no_predicate = False
            self.w_predicate = w_predicate
        self.iterable = space.iter(w_iterable)

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        while True:
            w_obj = self.space.next(self.iterable)  # may raise w_StopIteration
            if self.no_predicate:
                pred = self.space.is_true(w_obj)
            else:
                w_pred = self.space.call_function(self.w_predicate, w_obj)
                pred = self.space.is_true(w_pred)
            if pred ^ self.reverse:
                return w_obj


class W_IFilter(_IFilterBase):
    reverse = False

def W_IFilter___new__(space, w_subtype, w_predicate, w_iterable):
    r = space.allocate_instance(W_IFilter, w_subtype)
    r.__init__(space, w_predicate, w_iterable)
    return space.wrap(r)

W_IFilter.typedef = TypeDef(
        'ifilter',
        __module__ = 'itertools',
        __new__  = interp2app(W_IFilter___new__),
        __iter__ = interp2app(W_IFilter.iter_w),
        next     = interp2app(W_IFilter.next_w),
        __doc__  = """Make an iterator that filters elements from iterable returning
    only those for which the predicate is True.  If predicate is
    None, return the items that are true.

    Equivalent to :

    def ifilter:
        if predicate is None:
            predicate = bool
        for x in iterable:
            if predicate(x):
                yield x
    """)

class W_IFilterFalse(_IFilterBase):
    reverse = True

def W_IFilterFalse___new__(space, w_subtype, w_predicate, w_iterable):
    r = space.allocate_instance(W_IFilterFalse, w_subtype)
    r.__init__(space, w_predicate, w_iterable)
    return space.wrap(r)

W_IFilterFalse.typedef = TypeDef(
        'ifilterfalse',
        __module__ = 'itertools',
        __new__  = interp2app(W_IFilterFalse___new__),
        __iter__ = interp2app(W_IFilterFalse.iter_w),
        next     = interp2app(W_IFilterFalse.next_w),
        __doc__  = """Make an iterator that filters elements from iterable returning
    only those for which the predicate is False.  If predicate is
    None, return the items that are false.

    Equivalent to :

    def ifilterfalse(predicate, iterable):
        if predicate is None:
            predicate = bool
        for x in iterable:
            if not predicate(x):
                yield x
    """)

class W_ISlice(Wrappable):
    def __init__(self, space, w_iterable, w_startstop, args_w):
        self.iterable = space.iter(w_iterable)
        self.space = space

        num_args = len(args_w)

        if num_args == 0:
            start = 0
            w_stop = w_startstop
        elif num_args <= 2:
            if space.is_w(w_startstop, space.w_None):
                start = 0
            else:
                start = space.int_w(w_startstop)
            w_stop = args_w[0]
        else:
            raise OperationError(space.w_TypeError, space.wrap("islice() takes at most 4 arguments (" + str(num_args) + " given)"))

        if space.is_w(w_stop, space.w_None):
            stop = -1
            stoppable = False
        else:
            stop = space.int_w(w_stop)
            stoppable = True

        if num_args == 2:
            w_step = args_w[1]
            if space.is_w(w_step, space.w_None):
                step = 1
            else:
                step = space.int_w(w_step)
        else:
            step = 1

        if start < 0:
            raise OperationError(space.w_ValueError, space.wrap("Indicies for islice() must be non-negative integers."))
        if stoppable and stop < 0:
            raise OperationError(space.w_ValueError, space.wrap("Stop argument must be a non-negative integer or None."))
        if step < 1:
            raise OperationError(space.w_ValueError, space.wrap("Step must be one or lager for islice()."))

        self.start = start
        self.stop = stop
        self.step = step

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        if self.start >= 0:               # first call only
            consume = self.start + 1
            self.start = -1
        else:                             # all following calls
            consume = self.step
        if self.stop >= 0:
            if self.stop < consume:
                raise OperationError(self.space.w_StopIteration,
                                     self.space.w_None)
            self.stop -= consume
        while True:
            w_obj = self.space.next(self.iterable)
            consume -= 1
            if consume <= 0:
                return w_obj

def W_ISlice___new__(space, w_subtype, w_iterable, w_startstop, args_w):
    r = space.allocate_instance(W_ISlice, w_subtype)
    r.__init__(space, w_iterable, w_startstop, args_w)
    return space.wrap(r)

W_ISlice.typedef = TypeDef(
        'islice',
        __module__ = 'itertools',
        __new__  = interp2app(W_ISlice___new__),
        __iter__ = interp2app(W_ISlice.iter_w),
        next     = interp2app(W_ISlice.next_w),
        __doc__  = """Make an iterator that returns selected elements from the
    iterable.  If start is non-zero, then elements from the iterable
    are skipped until start is reached. Afterward, elements are
    returned consecutively unless step is set higher than one which
    results in items being skipped. If stop is None, then iteration
    continues until the iterator is exhausted, if at all; otherwise,
    it stops at the specified position. Unlike regular slicing,
    islice() does not support negative values for start, stop, or
    step. Can be used to extract related fields from data where the
    internal structure has been flattened (for example, a multi-line
    report may list a name field on every third line).
    """)


class W_Chain(Wrappable):
    def __init__(self, space, w_iterables):
        self.space = space
        self.w_iterables = w_iterables
        self.w_it = None

    def iter_w(self):
        return self.space.wrap(self)

    def _advance(self):
        self.w_it = self.space.iter(self.space.next(self.w_iterables))

    def next_w(self):
        if not self.w_iterables:
            # already stopped
            raise OperationError(self.space.w_StopIteration, self.space.w_None)
        if not self.w_it:
            self._advance()
        try:
            return self.space.next(self.w_it)
        except OperationError, e:
            return self._handle_error(e)

    def _handle_error(self, e):
        while True:
            if not e.match(self.space, self.space.w_StopIteration):
                raise e
            self._advance() # may raise StopIteration itself
            try:
                return self.space.next(self.w_it)
            except OperationError, e:
                pass # loop back to the start of _handle_error(e)

def W_Chain___new__(space, w_subtype, args_w):
    r = space.allocate_instance(W_Chain, w_subtype)
    w_args = space.newtuple(args_w)
    r.__init__(space, space.iter(w_args))
    return space.wrap(r)

def chain_from_iterable(space, w_cls, w_arg):
    """chain.from_iterable(iterable) --> chain object

    Alternate chain() contructor taking a single iterable argument
    that evaluates lazily."""
    r = space.allocate_instance(W_Chain, w_cls)
    r.__init__(space, space.iter(w_arg))
    return space.wrap(r)

W_Chain.typedef = TypeDef(
        'chain',
        __module__ = 'itertools',
        __new__  = interp2app(W_Chain___new__),
        __iter__ = interp2app(W_Chain.iter_w),
        next     = interp2app(W_Chain.next_w),
        from_iterable = interp2app(chain_from_iterable, as_classmethod=True),
        __doc__  = """Make an iterator that returns elements from the first iterable
    until it is exhausted, then proceeds to the next iterable, until
    all of the iterables are exhausted. Used for treating consecutive
    sequences as a single sequence.

    Equivalent to :

    def chain(*iterables):
        for it in iterables:
            for element in it:
                yield element
    """)

class W_IMap(Wrappable):
    _error_name = "imap"
    _immutable_fields_ = ["w_fun", "iterators_w"]

    def __init__(self, space, w_fun, args_w):
        self.space = space
        if self.space.is_w(w_fun, space.w_None):
            self.w_fun = None
        else:
            self.w_fun = w_fun

        iterators_w = []
        i = 0
        for iterable_w in args_w:
            try:
                iterator_w = space.iter(iterable_w)
            except OperationError, e:
                if e.match(self.space, self.space.w_TypeError):
                    raise OperationError(space.w_TypeError, space.wrap(self._error_name + " argument #" + str(i + 1) + " must support iteration"))
                else:
                    raise
            else:
                iterators_w.append(iterator_w)

            i += 1

        self.iterators_w = iterators_w

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        # common case: 1 or 2 arguments
        iterators_w = self.iterators_w
        length = len(iterators_w)
        if length == 1:
            objects = [self.space.next(iterators_w[0])]
        elif length == 2:
            objects = [self.space.next(iterators_w[0]),
                       self.space.next(iterators_w[1])]
        else:
            objects = self._get_objects()
        w_objects = self.space.newtuple(objects)
        if self.w_fun is None:
            return w_objects
        else:
            return self.space.call(self.w_fun, w_objects)

    def _get_objects(self):
        # the loop is out of the way of the JIT
        return [self.space.next(w_elem) for w_elem in self.iterators_w]


def W_IMap___new__(space, w_subtype, w_fun, args_w):
    if len(args_w) == 0:
        raise OperationError(space.w_TypeError,
                  space.wrap("imap() must have at least two arguments"))
    r = space.allocate_instance(W_IMap, w_subtype)
    r.__init__(space, w_fun, args_w)
    return space.wrap(r)

W_IMap.typedef = TypeDef(
        'imap',
        __module__ = 'itertools',
        __new__  = interp2app(W_IMap___new__),
        __iter__ = interp2app(W_IMap.iter_w),
        next     = interp2app(W_IMap.next_w),
        __doc__  = """Make an iterator that computes the function using arguments
    from each of the iterables. If function is set to None, then
    imap() returns the arguments as a tuple. Like map() but stops
    when the shortest iterable is exhausted instead of filling in
    None for shorter iterables. The reason for the difference is that
    infinite iterator arguments are typically an error for map()
    (because the output is fully evaluated) but represent a common
    and useful way of supplying arguments to imap().

    Equivalent to :

    def imap(function, *iterables):
        iterables = map(iter, iterables)
        while True:
            args = [i.next() for i in iterables]
            if function is None:
                yield tuple(args)
            else:
                yield function(*args)

    """)


class W_IZip(W_IMap):
    _error_name = "izip"

    def next_w(self):
        # argh.  izip(*args) is almost like imap(None, *args) except
        # that the former needs a special case for len(args)==0
        # while the latter just raises a TypeError in this situation.
        if len(self.iterators_w) == 0:
            raise OperationError(self.space.w_StopIteration, self.space.w_None)
        return W_IMap.next_w(self)

def W_IZip___new__(space, w_subtype, args_w):
    r = space.allocate_instance(W_IZip, w_subtype)
    r.__init__(space, space.w_None, args_w)
    return space.wrap(r)

W_IZip.typedef = TypeDef(
        'izip',
        __module__ = 'itertools',
        __new__  = interp2app(W_IZip___new__),
        __iter__ = interp2app(W_IZip.iter_w),
        next     = interp2app(W_IZip.next_w),
        __doc__  = """Make an iterator that aggregates elements from each of the
    iterables.  Like zip() except that it returns an iterator instead
    of a list. Used for lock-step iteration over several iterables at
    a time.

    Equivalent to :

    def izip(*iterables):
        iterables = map(iter, iterables)
        while iterables:
            result = [i.next() for i in iterables]
            yield tuple(result)
    """)


class W_IZipLongest(W_IMap):
    _error_name = "izip_longest"

    def next_w(self):
        space = self.space
        nb = len(self.iterators_w)

        if nb == 0:
            raise OperationError(space.w_StopIteration, space.w_None)

        objects_w = [None] * nb
        for index in range(nb):
            w_value = self.w_fillvalue
            w_it = self.iterators_w[index]
            if w_it is not None:
                try:
                    w_value = space.next(w_it)
                except OperationError, e:
                    if not e.match(space, space.w_StopIteration):
                        raise

                    self.active -= 1
                    if self.active == 0:
                        # It was the last active iterator
                        raise
                    self.iterators_w[index] = None

            objects_w[index] = w_value
        return space.newtuple(objects_w)

def W_IZipLongest___new__(space, w_subtype, __args__):
    arguments_w, kwds_w = __args__.unpack()
    w_fillvalue = space.w_None
    if kwds_w:
        if "fillvalue" in kwds_w:
            w_fillvalue = kwds_w["fillvalue"]
            del kwds_w["fillvalue"]
        if kwds_w:
            raise OperationError(space.w_TypeError, space.wrap(
                "izip_longest() got unexpected keyword argument(s)"))

    self = space.allocate_instance(W_IZipLongest, w_subtype)
    self.__init__(space, space.w_None, arguments_w)
    self.w_fillvalue = w_fillvalue
    self.active = len(self.iterators_w)

    return space.wrap(self)

W_IZipLongest.typedef = TypeDef(
        'izip_longest',
        __module__ = 'itertools',
        __new__  = interp2app(W_IZipLongest___new__),
        __iter__ = interp2app(W_IZipLongest.iter_w),
        next     = interp2app(W_IZipLongest.next_w),
        __doc__  = """Return an izip_longest object whose .next() method returns a tuple where
    the i-th element comes from the i-th iterable argument.  The .next()
    method continues until the longest iterable in the argument sequence
    is exhausted and then it raises StopIteration.  When the shorter iterables
    are exhausted, the fillvalue is substituted in their place.  The fillvalue
    defaults to None or can be specified by a keyword argument.
    """)


class W_Cycle(Wrappable):

    def __init__(self, space, w_iterable):
        self.space = space
        self.saved_w = []
        self.w_iterable = space.iter(w_iterable)
        self.index = 0
        self.exhausted = False

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        if self.exhausted:
            if not self.saved_w:
                raise OperationError(self.space.w_StopIteration, self.space.w_None)
            try:
                w_obj = self.saved_w[self.index]
            except IndexError:
                self.index = 1
                w_obj = self.saved_w[0]
            else:
                self.index += 1
        else:
            try:
                w_obj = self.space.next(self.w_iterable)
            except OperationError, e:
                if e.match(self.space, self.space.w_StopIteration):
                    self.exhausted = True
                    if not self.saved_w:
                        raise
                    self.index = 1
                    w_obj = self.saved_w[0]
                else:
                    raise
            else:
                self.index += 1
                self.saved_w.append(w_obj)
        return w_obj

def W_Cycle___new__(space, w_subtype, w_iterable):
    r = space.allocate_instance(W_Cycle, w_subtype)
    r.__init__(space, w_iterable)
    return space.wrap(r)

W_Cycle.typedef = TypeDef(
        'cycle',
        __module__ = 'itertools',
        __new__  = interp2app(W_Cycle___new__),
        __iter__ = interp2app(W_Cycle.iter_w),
        next     = interp2app(W_Cycle.next_w),
        __doc__  = """Make an iterator returning elements from the iterable and
    saving a copy of each. When the iterable is exhausted, return
    elements from the saved copy. Repeats indefinitely.

    Equivalent to :

    def cycle(iterable):
        saved = []
        for element in iterable:
            yield element
            saved.append(element)
        while saved:
            for element in saved:
                yield element
    """)

class W_StarMap(Wrappable):

    def __init__(self, space, w_fun, w_iterable):
        self.space = space
        self.w_fun = w_fun
        self.w_iterable = self.space.iter(w_iterable)

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        w_obj = self.space.next(self.w_iterable)
        return self.space.call(self.w_fun, w_obj)

def W_StarMap___new__(space, w_subtype, w_fun, w_iterable):
    r = space.allocate_instance(W_StarMap, w_subtype)
    r.__init__(space, w_fun, w_iterable)
    return space.wrap(r)

W_StarMap.typedef = TypeDef(
        'starmap',
        __module__ = 'itertools',
        __new__  = interp2app(W_StarMap___new__),
        __iter__ = interp2app(W_StarMap.iter_w),
        next     = interp2app(W_StarMap.next_w),
        __doc__  = """Make an iterator that computes the function using arguments
    tuples obtained from the iterable. Used instead of imap() when
    argument parameters are already grouped in tuples from a single
    iterable (the data has been ``pre-zipped''). The difference
    between imap() and starmap() parallels the distinction between
    function(a,b) and function(*c).

    Equivalent to :

    def starmap(function, iterable):
        iterable = iter(iterable)
        while True:
            yield function(*iterable.next())
    """)


@unwrap_spec(n=int)
def tee(space, w_iterable, n=2):
    """Return n independent iterators from a single iterable.
    Note : once tee() has made a split, the original iterable
    should not be used anywhere else; otherwise, the iterable could get
    advanced without the tee objects being informed.

    Note : this member of the toolkit may require significant auxiliary
    storage (depending on how much temporary data needs to be stored).
    In general, if one iterator is going to use most or all of the
    data before the other iterator, it is faster to use list() instead
    of tee()

    Equivalent to :

    def tee(iterable, n=2):
        def gen(next, data={}, cnt=[0]):
            for i in count():
                if i == cnt[0]:
                    item = data[i] = next()
                    cnt[0] += 1
                else:
                    item = data.pop(i)
                yield item
        it = iter(iterable)
        return tuple([gen(it.next) for i in range(n)])
    """
    if n < 0:
        raise OperationError(space.w_ValueError, space.wrap("n must be >= 0"))

    myiter = space.interpclass_w(w_iterable)
    if isinstance(myiter, W_TeeIterable):     # optimization only
        tee_state = myiter.tee_state
        iterators_w = [w_iterable] * n
        for i in range(1, n):
            iterators_w[i] = space.wrap(W_TeeIterable(space, tee_state))
    else:
        tee_state = TeeState(space, w_iterable)
        iterators_w = [space.wrap(W_TeeIterable(space, tee_state)) for x in range(n)]
    return space.newtuple(iterators_w)

class TeeState(object):
    def __init__(self, space, w_iterable):
        self.space = space
        self.w_iterable = self.space.iter(w_iterable)
        self.num_saved = 0
        self.saved_w = []

    def get_next(self, index):
        if index >= self.num_saved:
            w_obj = self.space.next(self.w_iterable)
            self.saved_w.append(w_obj)
            self.num_saved += 1
            return w_obj
        else:
            return self.saved_w[index]

class W_TeeIterable(Wrappable):
    def __init__(self, space, tee_state):
        self.space = space
        self.tee_state = tee_state
        self.index = 0

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        try:
            w_obj = self.tee_state.get_next(self.index)
            return w_obj
        finally:
            self.index += 1

def W_TeeIterable___new__(space, w_subtype, w_iterable):
    # Obscure and undocumented function.  PyPy only supports w_iterable
    # being a W_TeeIterable, because the case where it is a general
    # iterable is useless and confusing as far as I can tell (as the
    # semantics are then slightly different; see the XXX in lib-python's
    # test_itertools).
    myiter = space.interp_w(W_TeeIterable, w_iterable)
    tee_state = myiter.tee_state
    return space.wrap(W_TeeIterable(space, tee_state))

W_TeeIterable.typedef = TypeDef(
        '_tee',
        __module__ = 'itertools',
        __new__ = interp2app(W_TeeIterable___new__),
        __iter__ = interp2app(W_TeeIterable.iter_w),
        next     = interp2app(W_TeeIterable.next_w),
        __weakref__ = make_weakref_descr(W_TeeIterable),
        )
W_TeeIterable.typedef.acceptable_as_base_class = False


class W_GroupBy(Wrappable):

    def __init__(self, space, w_iterable, w_fun):
        self.space = space
        self.w_iterable = self.space.iter(w_iterable)
        self.identity_fun = self.space.is_w(w_fun, self.space.w_None)
        self.w_fun = w_fun
        self.index = 0
        self.lookahead = False
        self.exhausted = False
        self.started = False
        # new_group - new group not started yet, next should not skip any items
        self.new_group = True
        self.w_lookahead = self.space.w_None
        self.w_key = self.space.w_None

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        if self.exhausted:
            raise OperationError(self.space.w_StopIteration, self.space.w_None)

        if not self.new_group:
            self._consume_unwanted_input()

        if not self.started:
            self.started = True
            try:
                w_obj = self.space.next(self.w_iterable)
            except OperationError, e:
                if e.match(self.space, self.space.w_StopIteration):
                    self.exhausted = True
                raise
            else:
                self.w_lookahead = w_obj
                if self.identity_fun:
                    self.w_key = w_obj
                else:
                    self.w_key = self.space.call_function(self.w_fun, w_obj)
                self.lookahead = True

        self.new_group = False
        w_iterator = self.space.wrap(W_GroupByIterator(self.space, self.index, self))
        return self.space.newtuple([self.w_key, w_iterator])

    def _consume_unwanted_input(self):
        # Consume unwanted input until we reach the next group
        try:
            while True:
                self.group_next(self.index)
        except StopIteration:
            pass
        if self.exhausted:
            raise OperationError(self.space.w_StopIteration, self.space.w_None)

    def group_next(self, group_index):
        if group_index < self.index:
            raise StopIteration
        else:
            if self.lookahead:
                self.lookahead = False
                return self.w_lookahead

            try:
                w_obj = self.space.next(self.w_iterable)
            except OperationError, e:
                if e.match(self.space, self.space.w_StopIteration):
                    self.exhausted = True
                    raise StopIteration
                else:
                    raise
            else:
                if self.identity_fun:
                    w_new_key = w_obj
                else:
                    w_new_key = self.space.call_function(self.w_fun, w_obj)
                if self.space.eq_w(self.w_key, w_new_key):
                    return w_obj
                else:
                    self.index += 1
                    self.w_lookahead = w_obj
                    self.w_key = w_new_key
                    self.lookahead = True
                    self.new_group = True #new group
                    raise StopIteration

def W_GroupBy___new__(space, w_subtype, w_iterable, w_key=None):
    r = space.allocate_instance(W_GroupBy, w_subtype)
    r.__init__(space, w_iterable, w_key)
    return space.wrap(r)

W_GroupBy.typedef = TypeDef(
        'groupby',
        __module__ = 'itertools',
        __new__  = interp2app(W_GroupBy___new__),
        __iter__ = interp2app(W_GroupBy.iter_w),
        next     = interp2app(W_GroupBy.next_w),
        __doc__  = """Make an iterator that returns consecutive keys and groups from the
    iterable. The key is a function computing a key value for each
    element. If not specified or is None, key defaults to an identity
    function and returns the element unchanged. Generally, the
    iterable needs to already be sorted on the same key function.

    The returned group is itself an iterator that shares the
    underlying iterable with groupby(). Because the source is shared,
    when the groupby object is advanced, the previous group is no
    longer visible. So, if that data is needed later, it should be
    stored as a list:

       groups = []
       uniquekeys = []
       for k, g in groupby(data, keyfunc):
           groups.append(list(g))      # Store group iterator as a list
           uniquekeys.append(k)
    """)

class W_GroupByIterator(Wrappable):
    def __init__(self, space, index, groupby):
        self.space = space
        self.index = index
        self.groupby = groupby
        self.exhausted = False

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        if self.exhausted:
            raise OperationError(self.space.w_StopIteration, self.space.w_None)

        try:
            w_obj = self.groupby.group_next(self.index)
        except StopIteration:
            self.exhausted = True
            raise OperationError(self.space.w_StopIteration, self.space.w_None)
        else:
            return w_obj

W_GroupByIterator.typedef = TypeDef(
        '_groupby',
        __module__ = 'itertools',
        __iter__ = interp2app(W_GroupByIterator.iter_w),
        next     = interp2app(W_GroupByIterator.next_w))
W_GroupByIterator.typedef.acceptable_as_base_class = False


class W_Compress(Wrappable):
    def __init__(self, space, w_data, w_selectors):
        self.space = space
        self.w_data = space.iter(w_data)
        self.w_selectors = space.iter(w_selectors)

    def iter_w(self):
        return self.space.wrap(self)

    def next_w(self):
        # No need to check for StopIteration since either w_data
        # or w_selectors will raise this. The shortest one stops first.
        while True:
            w_next_item = self.space.next(self.w_data)
            w_next_selector = self.space.next(self.w_selectors)
            if self.space.is_true(w_next_selector):
                return w_next_item


def W_Compress__new__(space, w_subtype, w_data, w_selectors):
    r = space.allocate_instance(W_Compress, w_subtype)
    r.__init__(space, w_data, w_selectors)
    return space.wrap(r)

W_Compress.typedef = TypeDef(
    'compress',
    __module__ = 'itertools',
    __new__ = interp2app(W_Compress__new__),
    __iter__ = interp2app(W_Compress.iter_w),
    next     = interp2app(W_Compress.next_w),
    __doc__ = """Make an iterator that filters elements from *data* returning
   only those that have a corresponding element in *selectors* that evaluates to
   ``True``.  Stops when either the *data* or *selectors* iterables has been
   exhausted.
   Equivalent to::

       def compress(data, selectors):
           # compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F
           return (d for d, s in izip(data, selectors) if s)
""")


class W_Product(Wrappable):
    def __init__(self, space, args_w, w_repeat):
        self.gears = [
            space.fixedview(arg_w) for arg_w in args_w
        ] * space.int_w(w_repeat)
        self.num_gears = len(self.gears)
        # initialization of indicies to loop over
        self.indicies = [
            (0, len(gear))
            for gear in self.gears
        ]
        self.cont = True
        for _, lim in self.indicies:
            if lim <= 0:
                self.cont = False
                break

    def roll_gears(self):
        if self.num_gears == 0:
            self.cont = False
            return

        # Starting from the end of the gear indicies work to the front
        # incrementing the gear until the limit is reached. When the limit
        # is reached carry operation to the next gear
        should_carry = True

        for n in range(0, self.num_gears):
            nth_gear = self.num_gears - n - 1
            if should_carry:
                count, lim = self.indicies[nth_gear]
                count += 1
                if count == lim and nth_gear == 0:
                    self.cont = False
                if count == lim:
                    should_carry = True
                    count = 0
                else:
                    should_carry = False
                self.indicies[nth_gear] = (count, lim)
            else:
                break

    def iter_w(self, space):
        return space.wrap(self)

    def next_w(self, space):
        if not self.cont:
            raise OperationError(space.w_StopIteration, space.w_None)
        l = [None] * self.num_gears
        for x in range(0, self.num_gears):
            index, limit = self.indicies[x]
            l[x] = self.gears[x][index]
        self.roll_gears()
        return space.newtuple(l)


def W_Product__new__(space, w_subtype, __args__):
    arguments_w, kwds_w = __args__.unpack()
    w_repeat = space.wrap(1)
    if kwds_w:
        if 'repeat' in kwds_w:
            w_repeat = kwds_w['repeat']
            del kwds_w['repeat']
        if kwds_w:
            raise OperationError(space.w_TypeError, space.wrap(
                "product() got unexpected keyword argument(s)"))

    r = space.allocate_instance(W_Product, w_subtype)
    r.__init__(space, arguments_w, w_repeat)
    return space.wrap(r)

W_Product.typedef = TypeDef(
    'product',
    __module__ = 'itertools',
    __new__ = interp2app(W_Product__new__),
    __iter__ = interp2app(W_Product.iter_w),
    next = interp2app(W_Product.next_w),
    __doc__ = """
   Cartesian product of input iterables.

   Equivalent to nested for-loops in a generator expression. For example,
   ``product(A, B)`` returns the same as ``((x,y) for x in A for y in B)``.

   The nested loops cycle like an odometer with the rightmost element advancing
   on every iteration.  This pattern creates a lexicographic ordering so that if
   the input's iterables are sorted, the product tuples are emitted in sorted
   order.

   To compute the product of an iterable with itself, specify the number of
   repetitions with the optional *repeat* keyword argument.  For example,
   ``product(A, repeat=4)`` means the same as ``product(A, A, A, A)``.

   This function is equivalent to the following code, except that the
   actual implementation does not build up intermediate results in memory::

       def product(*args, **kwds):
           # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
           # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
           pools = map(tuple, args) * kwds.get('repeat', 1)
           result = [[]]
           for pool in pools:
               result = [x+[y] for x in result for y in pool]
           for prod in result:
               yield tuple(prod)
""")


class W_Combinations(Wrappable):
    def __init__(self, space, pool_w, indices, r):
        self.pool_w = pool_w
        self.indices = indices
        self.r = r
        self.last_result_w = None
        self.stopped = r > len(pool_w)

    def get_maximum(self, i):
        return i + len(self.pool_w) - self.r

    def max_index(self, j):
        return self.indices[j - 1] + 1

    def descr__iter__(self, space):
        return self

    def descr_next(self, space):
        if self.stopped:
            raise OperationError(space.w_StopIteration, space.w_None)
        if self.last_result_w is None:
            # On the first pass, initialize result tuple using the indices
            result_w = [None] * self.r
            for i in xrange(self.r):
                index = self.indices[i]
                result_w[i] = self.pool_w[index]
        else:
            # Copy the previous result
            result_w = self.last_result_w[:]
            # Scan indices right-to-left until finding one that is not at its
            # maximum
            i = self.r - 1
            while i >= 0 and self.indices[i] == self.get_maximum(i):
                i -= 1

            # If i is negative, then the indices are all at their maximum value
            # and we're done
            if i < 0:
                self.stopped = True
                raise OperationError(space.w_StopIteration, space.w_None)

            # Increment the current index which we know is not at its maximum.
            # Then move back to the right setting each index to its lowest
            # possible value
            self.indices[i] += 1
            for j in xrange(i + 1, self.r):
                self.indices[j] = self.max_index(j)

            # Update the result for the new indices starting with i, the
            # leftmost index that changed
            for i in xrange(i, self.r):
                index = self.indices[i]
                w_elem = self.pool_w[index]
                result_w[i] = w_elem
        self.last_result_w = result_w
        return space.newtuple(result_w)

@unwrap_spec(r=int)
def W_Combinations__new__(space, w_subtype, w_iterable, r):
    pool_w = space.fixedview(w_iterable)
    if r < 0:
        raise OperationError(space.w_ValueError,
            space.wrap("r must be non-negative")
        )
    indices = range(len(pool_w))
    res = space.allocate_instance(W_Combinations, w_subtype)
    res.__init__(space, pool_w, indices, r)
    return space.wrap(res)

W_Combinations.typedef = TypeDef("combinations",
    __module__ = 'itertools',
    __new__ = interp2app(W_Combinations__new__),
    __iter__ = interp2app(W_Combinations.descr__iter__),
    next = interp2app(W_Combinations.descr_next),
    __doc__ = """\
combinations(iterable, r) --> combinations object

Return successive r-length combinations of elements in the iterable.

combinations(range(4), 3) --> (0,1,2), (0,1,3), (0,2,3), (1,2,3)""",
)

class W_CombinationsWithReplacement(W_Combinations):
    def __init__(self, space, pool_w, indices, r):
        W_Combinations.__init__(self, space, pool_w, indices, r)
        self.stopped = len(pool_w) == 0 and r > 0

    def get_maximum(self, i):
        return len(self.pool_w) - 1

    def max_index(self, j):
        return self.indices[j - 1]

@unwrap_spec(r=int)
def W_CombinationsWithReplacement__new__(space, w_subtype, w_iterable, r):
    pool_w = space.fixedview(w_iterable)
    if r < 0:
        raise OperationError(space.w_ValueError,
                             space.wrap("r must be non-negative"))
    indices = [0] * r
    res = space.allocate_instance(W_CombinationsWithReplacement, w_subtype)
    res.__init__(space, pool_w, indices, r)
    return space.wrap(res)

W_CombinationsWithReplacement.typedef = TypeDef("combinations_with_replacement",
    __module__ = 'itertools',
    __new__ = interp2app(W_CombinationsWithReplacement__new__),
    __iter__ = interp2app(W_CombinationsWithReplacement.descr__iter__),
    next = interp2app(W_CombinationsWithReplacement.descr_next),
    __doc__ = """\
combinations_with_replacement(iterable, r) --> combinations_with_replacement object

Return successive r-length combinations of elements in the iterable
allowing individual elements to have successive repeats.
combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC""",
)


class W_Permutations(Wrappable):
    def __init__(self, space, pool_w, r):
        self.pool_w = pool_w
        self.r = r
        n = len(pool_w)
        n_minus_r = n - r
        if n_minus_r < 0:
            self.stopped = True
        else:
            self.stopped = False
            self.indices = range(n)
            self.cycles = range(n, n_minus_r, -1)

    def descr__iter__(self, space):
        return self

    def descr_next(self, space):
        if self.stopped:
            raise OperationError(space.w_StopIteration, space.w_None)
        r = self.r
        indices = self.indices
        w_result = space.newtuple([self.pool_w[indices[i]]
                                   for i in range(r)])
        cycles = self.cycles
        i = r - 1
        while i >= 0:
            j = cycles[i] - 1
            if j > 0:
                cycles[i] = j
                indices[i], indices[-j] = indices[-j], indices[i]
                return w_result
            cycles[i] = len(indices) - i
            n1 = len(indices) - 1
            assert n1 >= 0
            num = indices[i]
            for k in range(i, n1):
                indices[k] = indices[k+1]
            indices[n1] = num
            i -= 1
        self.stopped = True
        return w_result

def W_Permutations__new__(space, w_subtype, w_iterable, w_r=None):
    pool_w = space.fixedview(w_iterable)
    if space.is_w(w_r, space.w_None):
        r = len(pool_w)
    else:
        r = space.gateway_nonnegint_w(w_r)
    res = space.allocate_instance(W_Permutations, w_subtype)
    res.__init__(space, pool_w, r)
    return space.wrap(res)

W_Permutations.typedef = TypeDef("permutations",
    __module__ = 'itertools',
    __new__ = interp2app(W_Permutations__new__),
    __iter__ = interp2app(W_Permutations.descr__iter__),
    next = interp2app(W_Permutations.descr_next),
    __doc__ = """\
permutations(iterable[, r]) --> permutations object

Return successive r-length permutations of elements in the iterable.

permutations(range(3), 2) --> (0,1), (0,2), (1,0), (1,2), (2,0), (2,1)""",
)