summaryrefslogtreecommitdiff
path: root/src/engine/SCons/Util.py
blob: c1f87a2e7868e59b31ea43f266a12560a359888d (plain)
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
"""SCons.Util

Various utility functions go here.
"""
#
# Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 The SCons Foundation
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be included
# in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

__revision__ = "src/engine/SCons/Util.py issue-2856:2676:d23b7a2f45e8 2012/08/05 15:38:28 garyo"

import os
import sys
import copy
import re
import types

from collections import UserDict, UserList, UserString

# Don't "from types import ..." these because we need to get at the
# types module later to look for UnicodeType.
InstanceType    = types.InstanceType
MethodType      = types.MethodType
FunctionType    = types.FunctionType
try: unicode
except NameError: UnicodeType = None
else:             UnicodeType = unicode

def dictify(keys, values, result={}):
    for k, v in zip(keys, values):
        result[k] = v
    return result

_altsep = os.altsep
if _altsep is None and sys.platform == 'win32':
    # My ActivePython 2.0.1 doesn't set os.altsep!  What gives?
    _altsep = '/'
if _altsep:
    def rightmost_separator(path, sep):
        return max(path.rfind(sep), path.rfind(_altsep))
else:
    def rightmost_separator(path, sep):
        return path.rfind(sep)

# First two from the Python Cookbook, just for completeness.
# (Yeah, yeah, YAGNI...)
def containsAny(str, set):
    """Check whether sequence str contains ANY of the items in set."""
    for c in set:
        if c in str: return 1
    return 0

def containsAll(str, set):
    """Check whether sequence str contains ALL of the items in set."""
    for c in set:
        if c not in str: return 0
    return 1

def containsOnly(str, set):
    """Check whether sequence str contains ONLY items in set."""
    for c in str:
        if c not in set: return 0
    return 1

def splitext(path):
    "Same as os.path.splitext() but faster."
    sep = rightmost_separator(path, os.sep)
    dot = path.rfind('.')
    # An ext is only real if it has at least one non-digit char
    if dot > sep and not containsOnly(path[dot:], "0123456789."):
        return path[:dot],path[dot:]
    else:
        return path,""

def updrive(path):
    """
    Make the drive letter (if any) upper case.
    This is useful because Windows is inconsitent on the case
    of the drive letter, which can cause inconsistencies when
    calculating command signatures.
    """
    drive, rest = os.path.splitdrive(path)
    if drive:
        path = drive.upper() + rest
    return path

class NodeList(UserList):
    """This class is almost exactly like a regular list of Nodes
    (actually it can hold any object), with one important difference.
    If you try to get an attribute from this list, it will return that
    attribute from every item in the list.  For example:

    >>> someList = NodeList([ '  foo  ', '  bar  ' ])
    >>> someList.strip()
    [ 'foo', 'bar' ]
    """
    def __nonzero__(self):
        return len(self.data) != 0

    def __str__(self):
        return ' '.join(map(str, self.data))

    def __iter__(self):
        return iter(self.data)

    def __call__(self, *args, **kwargs):
        result = [x(*args, **kwargs) for x in self.data]
        return self.__class__(result)

    def __getattr__(self, name):
        result = [getattr(x, name) for x in self.data]
        return self.__class__(result)


_get_env_var = re.compile(r'^\$([_a-zA-Z]\w*|{[_a-zA-Z]\w*})$')

def get_environment_var(varstr):
    """Given a string, first determine if it looks like a reference
    to a single environment variable, like "$FOO" or "${FOO}".
    If so, return that variable with no decorations ("FOO").
    If not, return None."""
    mo=_get_env_var.match(to_String(varstr))
    if mo:
        var = mo.group(1)
        if var[0] == '{':
            return var[1:-1]
        else:
            return var
    else:
        return None

class DisplayEngine(object):
    print_it = True
    def __call__(self, text, append_newline=1):
        if not self.print_it:
            return
        if append_newline: text = text + '\n'
        try:
            sys.stdout.write(unicode(text))
        except IOError:
            # Stdout might be connected to a pipe that has been closed
            # by now. The most likely reason for the pipe being closed
            # is that the user has press ctrl-c. It this is the case,
            # then SCons is currently shutdown. We therefore ignore
            # IOError's here so that SCons can continue and shutdown
            # properly so that the .sconsign is correctly written
            # before SCons exits.
            pass

    def set_mode(self, mode):
        self.print_it = mode

def render_tree(root, child_func, prune=0, margin=[0], visited={}):
    """
    Render a tree of nodes into an ASCII tree view.
    root - the root node of the tree
    child_func - the function called to get the children of a node
    prune - don't visit the same node twice
    margin - the format of the left margin to use for children of root.
       1 results in a pipe, and 0 results in no pipe.
    visited - a dictionary of visited nodes in the current branch if not prune,
       or in the whole tree if prune.
    """

    rname = str(root)

    children = child_func(root)
    retval = ""
    for pipe in margin[:-1]:
        if pipe:
            retval = retval + "| "
        else:
            retval = retval + "  "

    if rname in visited:
        return retval + "+-[" + rname + "]\n"

    retval = retval + "+-" + rname + "\n"
    if not prune:
        visited = copy.copy(visited)
    visited[rname] = 1

    for i in range(len(children)):
        margin.append(i<len(children)-1)
        retval = retval + render_tree(children[i], child_func, prune, margin, visited
)
        margin.pop()

    return retval

IDX = lambda N: N and 1 or 0

def print_tree(root, child_func, prune=0, showtags=0, margin=[0], visited={}):
    """
    Print a tree of nodes.  This is like render_tree, except it prints
    lines directly instead of creating a string representation in memory,
    so that huge trees can be printed.

    root - the root node of the tree
    child_func - the function called to get the children of a node
    prune - don't visit the same node twice
    showtags - print status information to the left of each node line
    margin - the format of the left margin to use for children of root.
       1 results in a pipe, and 0 results in no pipe.
    visited - a dictionary of visited nodes in the current branch if not prune,
       or in the whole tree if prune.
    """

    rname = str(root)

    if showtags:

        if showtags == 2:
            legend = (' E         = exists\n' +
                      '  R        = exists in repository only\n' +
                      '   b       = implicit builder\n' +
                      '   B       = explicit builder\n' +
                      '    S      = side effect\n' +
                      '     P     = precious\n' +
                      '      A    = always build\n' +
                      '       C   = current\n' +
                      '        N  = no clean\n' +
                      '         H = no cache\n' +
                      '\n')
            sys.stdout.write(unicode(legend))

        tags = ['[']
        tags.append(' E'[IDX(root.exists())])
        tags.append(' R'[IDX(root.rexists() and not root.exists())])
        tags.append(' BbB'[[0,1][IDX(root.has_explicit_builder())] +
                           [0,2][IDX(root.has_builder())]])
        tags.append(' S'[IDX(root.side_effect)])
        tags.append(' P'[IDX(root.precious)])
        tags.append(' A'[IDX(root.always_build)])
        tags.append(' C'[IDX(root.is_up_to_date())])
        tags.append(' N'[IDX(root.noclean)])
        tags.append(' H'[IDX(root.nocache)])
        tags.append(']')

    else:
        tags = []

    def MMM(m):
        return ["  ","| "][m]
    margins = list(map(MMM, margin[:-1]))

    children = child_func(root)

    if prune and rname in visited and children:
        sys.stdout.write(''.join(tags + margins + ['+-[', rname, ']']) + u'\n')
        return

    sys.stdout.write(''.join(tags + margins + ['+-', rname]) + u'\n')

    visited[rname] = 1

    if children:
        margin.append(1)
        idx = IDX(showtags)
        for C in children[:-1]:
            print_tree(C, child_func, prune, idx, margin, visited)
        margin[-1] = 0
        print_tree(children[-1], child_func, prune, idx, margin, visited)
        margin.pop()



# Functions for deciding if things are like various types, mainly to
# handle UserDict, UserList and UserString like their underlying types.
#
# Yes, all of this manual testing breaks polymorphism, and the real
# Pythonic way to do all of this would be to just try it and handle the
# exception, but handling the exception when it's not the right type is
# often too slow.

# We are using the following trick to speed up these
# functions. Default arguments are used to take a snapshot of the
# the global functions and constants used by these functions. This
# transforms accesses to global variable into local variables
# accesses (i.e. LOAD_FAST instead of LOAD_GLOBAL).

DictTypes = (dict, UserDict)
ListTypes = (list, UserList)
SequenceTypes = (list, tuple, UserList)

# Note that profiling data shows a speed-up when comparing
# explicitely with str and unicode instead of simply comparing
# with basestring. (at least on Python 2.5.1)
StringTypes = (str, unicode, UserString)

# Empirically, it is faster to check explicitely for str and
# unicode than for basestring.
BaseStringTypes = (str, unicode)

def is_Dict(obj, isinstance=isinstance, DictTypes=DictTypes):
    return isinstance(obj, DictTypes)

def is_List(obj, isinstance=isinstance, ListTypes=ListTypes):
    return isinstance(obj, ListTypes)

def is_Sequence(obj, isinstance=isinstance, SequenceTypes=SequenceTypes):
    return isinstance(obj, SequenceTypes)

def is_Tuple(obj, isinstance=isinstance, tuple=tuple):
    return isinstance(obj, tuple)

def is_String(obj, isinstance=isinstance, StringTypes=StringTypes):
    return isinstance(obj, StringTypes)

def is_Scalar(obj, isinstance=isinstance, StringTypes=StringTypes, SequenceTypes=SequenceTypes):
    # Profiling shows that there is an impressive speed-up of 2x
    # when explicitely checking for strings instead of just not
    # sequence when the argument (i.e. obj) is already a string.
    # But, if obj is a not string then it is twice as fast to
    # check only for 'not sequence'. The following code therefore
    # assumes that the obj argument is a string must of the time.
    return isinstance(obj, StringTypes) or not isinstance(obj, SequenceTypes)

def do_flatten(sequence, result, isinstance=isinstance, 
               StringTypes=StringTypes, SequenceTypes=SequenceTypes):
    for item in sequence:
        if isinstance(item, StringTypes) or not isinstance(item, SequenceTypes):
            result.append(item)
        else:
            do_flatten(item, result)

def flatten(obj, isinstance=isinstance, StringTypes=StringTypes, 
            SequenceTypes=SequenceTypes, do_flatten=do_flatten):
    """Flatten a sequence to a non-nested list.

    Flatten() converts either a single scalar or a nested sequence
    to a non-nested list. Note that flatten() considers strings
    to be scalars instead of sequences like Python would.
    """
    if isinstance(obj, StringTypes) or not isinstance(obj, SequenceTypes):
        return [obj]
    result = []
    for item in obj:
        if isinstance(item, StringTypes) or not isinstance(item, SequenceTypes):
            result.append(item)
        else:
            do_flatten(item, result)
    return result

def flatten_sequence(sequence, isinstance=isinstance, StringTypes=StringTypes, 
                     SequenceTypes=SequenceTypes, do_flatten=do_flatten):
    """Flatten a sequence to a non-nested list.

    Same as flatten(), but it does not handle the single scalar
    case. This is slightly more efficient when one knows that
    the sequence to flatten can not be a scalar.
    """
    result = []
    for item in sequence:
        if isinstance(item, StringTypes) or not isinstance(item, SequenceTypes):
            result.append(item)
        else:
            do_flatten(item, result)
    return result

# Generic convert-to-string functions that abstract away whether or
# not the Python we're executing has Unicode support.  The wrapper
# to_String_for_signature() will use a for_signature() method if the
# specified object has one.
#
def to_String(s, 
              isinstance=isinstance, str=str,
              UserString=UserString, BaseStringTypes=BaseStringTypes):
    if isinstance(s,BaseStringTypes):
        # Early out when already a string!
        return s
    elif isinstance(s, UserString):
        # s.data can only be either a unicode or a regular
        # string. Please see the UserString initializer.
        return s.data
    else:
        return str(s)

def to_String_for_subst(s, 
                        isinstance=isinstance, str=str, to_String=to_String,
                        BaseStringTypes=BaseStringTypes, SequenceTypes=SequenceTypes,
                        UserString=UserString):
                        
    # Note that the test cases are sorted by order of probability.
    if isinstance(s, BaseStringTypes):
        return s
    elif isinstance(s, SequenceTypes):
        l = []
        for e in s:
            l.append(to_String_for_subst(e))
        return ' '.join( s )
    elif isinstance(s, UserString):
        # s.data can only be either a unicode or a regular
        # string. Please see the UserString initializer.
        return s.data
    else:
        return str(s)

def to_String_for_signature(obj, to_String_for_subst=to_String_for_subst, 
                            AttributeError=AttributeError):
    try:
        f = obj.for_signature
    except AttributeError:
        return to_String_for_subst(obj)
    else:
        return f()


# The SCons "semi-deep" copy.
#
# This makes separate copies of lists (including UserList objects)
# dictionaries (including UserDict objects) and tuples, but just copies
# references to anything else it finds.
#
# A special case is any object that has a __semi_deepcopy__() method,
# which we invoke to create the copy. Currently only used by
# BuilderDict to actually prevent the copy operation (as invalid on that object)
#
# The dispatch table approach used here is a direct rip-off from the
# normal Python copy module.

_semi_deepcopy_dispatch = d = {}

def semi_deepcopy_dict(x, exclude = [] ):
    copy = {}
    for key, val in x.items():
        # The regular Python copy.deepcopy() also deepcopies the key,
        # as follows:
        #
        #    copy[semi_deepcopy(key)] = semi_deepcopy(val)
        #
        # Doesn't seem like we need to, but we'll comment it just in case.
        if key not in exclude:
            copy[key] = semi_deepcopy(val)
    return copy
d[dict] = semi_deepcopy_dict

def _semi_deepcopy_list(x):
    return list(map(semi_deepcopy, x))
d[list] = _semi_deepcopy_list

def _semi_deepcopy_tuple(x):
    return tuple(map(semi_deepcopy, x))
d[tuple] = _semi_deepcopy_tuple

def semi_deepcopy(x):
    copier = _semi_deepcopy_dispatch.get(type(x))
    if copier:
        return copier(x)
    else:
        if hasattr(x, '__semi_deepcopy__') and callable(x.__semi_deepcopy__):
            return x.__semi_deepcopy__()
        elif isinstance(x, UserDict):
            return x.__class__(semi_deepcopy_dict(x))
        elif isinstance(x, UserList):
            return x.__class__(_semi_deepcopy_list(x))
        
        return x


class Proxy(object):
    """A simple generic Proxy class, forwarding all calls to
    subject.  So, for the benefit of the python newbie, what does
    this really mean?  Well, it means that you can take an object, let's
    call it 'objA', and wrap it in this Proxy class, with a statement
    like this

                 proxyObj = Proxy(objA),

    Then, if in the future, you do something like this

                 x = proxyObj.var1,

    since Proxy does not have a 'var1' attribute (but presumably objA does),
    the request actually is equivalent to saying

                 x = objA.var1

    Inherit from this class to create a Proxy.

    Note that, with new-style classes, this does *not* work transparently
    for Proxy subclasses that use special .__*__() method names, because
    those names are now bound to the class, not the individual instances.
    You now need to know in advance which .__*__() method names you want
    to pass on to the underlying Proxy object, and specifically delegate
    their calls like this:

        class Foo(Proxy):
            __str__ = Delegate('__str__')
    """

    def __init__(self, subject):
        """Wrap an object as a Proxy object"""
        self._subject = subject

    def __getattr__(self, name):
        """Retrieve an attribute from the wrapped object.  If the named
           attribute doesn't exist, AttributeError is raised"""
        return getattr(self._subject, name)

    def get(self):
        """Retrieve the entire wrapped object"""
        return self._subject

    def __cmp__(self, other):
        if issubclass(other.__class__, self._subject.__class__):
            return cmp(self._subject, other)
        return cmp(self.__dict__, other.__dict__)

class Delegate(object):
    """A Python Descriptor class that delegates attribute fetches
    to an underlying wrapped subject of a Proxy.  Typical use:

        class Foo(Proxy):
            __str__ = Delegate('__str__')
    """
    def __init__(self, attribute):
        self.attribute = attribute
    def __get__(self, obj, cls):
        if isinstance(obj, cls):
            return getattr(obj._subject, self.attribute)
        else:
            return self

# attempt to load the windows registry module:
can_read_reg = 0
try:
    import winreg

    can_read_reg = 1
    hkey_mod = winreg

    RegOpenKeyEx    = winreg.OpenKeyEx
    RegEnumKey      = winreg.EnumKey
    RegEnumValue    = winreg.EnumValue
    RegQueryValueEx = winreg.QueryValueEx
    RegError        = winreg.error

except ImportError:
    try:
        import win32api
        import win32con
        can_read_reg = 1
        hkey_mod = win32con

        RegOpenKeyEx    = win32api.RegOpenKeyEx
        RegEnumKey      = win32api.RegEnumKey
        RegEnumValue    = win32api.RegEnumValue
        RegQueryValueEx = win32api.RegQueryValueEx
        RegError        = win32api.error

    except ImportError:
        class _NoError(Exception):
            pass
        RegError = _NoError

if can_read_reg:
    HKEY_CLASSES_ROOT  = hkey_mod.HKEY_CLASSES_ROOT
    HKEY_LOCAL_MACHINE = hkey_mod.HKEY_LOCAL_MACHINE
    HKEY_CURRENT_USER  = hkey_mod.HKEY_CURRENT_USER
    HKEY_USERS         = hkey_mod.HKEY_USERS

    def RegGetValue(root, key):
        """This utility function returns a value in the registry
        without having to open the key first.  Only available on
        Windows platforms with a version of Python that can read the
        registry.  Returns the same thing as
        SCons.Util.RegQueryValueEx, except you just specify the entire
        path to the value, and don't have to bother opening the key
        first.  So:

        Instead of:
          k = SCons.Util.RegOpenKeyEx(SCons.Util.HKEY_LOCAL_MACHINE,
                r'SOFTWARE\Microsoft\Windows\CurrentVersion')
          out = SCons.Util.RegQueryValueEx(k,
                'ProgramFilesDir')

        You can write:
          out = SCons.Util.RegGetValue(SCons.Util.HKEY_LOCAL_MACHINE,
                r'SOFTWARE\Microsoft\Windows\CurrentVersion\ProgramFilesDir')
        """
        # I would use os.path.split here, but it's not a filesystem
        # path...
        p = key.rfind('\\') + 1
        keyp = key[:p-1]          # -1 to omit trailing slash
        val = key[p:]
        k = RegOpenKeyEx(root, keyp)
        return RegQueryValueEx(k,val)
else:
    try:
        e = WindowsError
    except NameError:
        # Make sure we have a definition of WindowsError so we can
        # run platform-independent tests of Windows functionality on
        # platforms other than Windows.  (WindowsError is, in fact, an
        # OSError subclass on Windows.)
        class WindowsError(OSError):
            pass
        import builtins
        builtins.WindowsError = WindowsError
    else:
        del e
        
    HKEY_CLASSES_ROOT = None
    HKEY_LOCAL_MACHINE = None
    HKEY_CURRENT_USER = None
    HKEY_USERS = None

    def RegGetValue(root, key):
        raise WindowsError

    def RegOpenKeyEx(root, key):
        raise WindowsError

if sys.platform == 'win32':

    def WhereIs(file, path=None, pathext=None, reject=[]):
        if path is None:
            try:
                path = os.environ['PATH']
            except KeyError:
                return None
        if is_String(path):
            path = path.split(os.pathsep)
        if pathext is None:
            try:
                pathext = os.environ['PATHEXT']
            except KeyError:
                pathext = '.COM;.EXE;.BAT;.CMD'
        if is_String(pathext):
            pathext = pathext.split(os.pathsep)
        for ext in pathext:
            if ext.lower() == file[-len(ext):].lower():
                pathext = ['']
                break
        if not is_List(reject) and not is_Tuple(reject):
            reject = [reject]
        for dir in path:
            f = os.path.join(dir, file)
            for ext in pathext:
                fext = f + ext
                if os.path.isfile(fext):
                    try:
                        reject.index(fext)
                    except ValueError:
                        return os.path.normpath(fext)
                    continue
        return None

elif os.name == 'os2':

    def WhereIs(file, path=None, pathext=None, reject=[]):
        if path is None:
            try:
                path = os.environ['PATH']
            except KeyError:
                return None
        if is_String(path):
            path = path.split(os.pathsep)
        if pathext is None:
            pathext = ['.exe', '.cmd']
        for ext in pathext:
            if ext.lower() == file[-len(ext):].lower():
                pathext = ['']
                break
        if not is_List(reject) and not is_Tuple(reject):
            reject = [reject]
        for dir in path:
            f = os.path.join(dir, file)
            for ext in pathext:
                fext = f + ext
                if os.path.isfile(fext):
                    try:
                        reject.index(fext)
                    except ValueError:
                        return os.path.normpath(fext)
                    continue
        return None

else:

    def WhereIs(file, path=None, pathext=None, reject=[]):
        import stat
        if path is None:
            try:
                path = os.environ['PATH']
            except KeyError:
                return None
        if is_String(path):
            path = path.split(os.pathsep)
        if not is_List(reject) and not is_Tuple(reject):
            reject = [reject]
        for d in path:
            f = os.path.join(d, file)
            if os.path.isfile(f):
                try:
                    st = os.stat(f)
                except OSError:
                    # os.stat() raises OSError, not IOError if the file
                    # doesn't exist, so in this case we let IOError get
                    # raised so as to not mask possibly serious disk or
                    # network issues.
                    continue
                if stat.S_IMODE(st[stat.ST_MODE]) & 0111:
                    try:
                        reject.index(f)
                    except ValueError:
                        return os.path.normpath(f)
                    continue
        return None

def PrependPath(oldpath, newpath, sep = os.pathsep, 
                delete_existing=1, canonicalize=None):
    """This prepends newpath elements to the given oldpath.  Will only
    add any particular path once (leaving the first one it encounters
    and ignoring the rest, to preserve path order), and will
    os.path.normpath and os.path.normcase all paths to help assure
    this.  This can also handle the case where the given old path
    variable is a list instead of a string, in which case a list will
    be returned instead of a string.

    Example:
      Old Path: "/foo/bar:/foo"
      New Path: "/biz/boom:/foo"
      Result:   "/biz/boom:/foo:/foo/bar"

    If delete_existing is 0, then adding a path that exists will
    not move it to the beginning; it will stay where it is in the
    list.

    If canonicalize is not None, it is applied to each element of 
    newpath before use.
    """

    orig = oldpath
    is_list = 1
    paths = orig
    if not is_List(orig) and not is_Tuple(orig):
        paths = paths.split(sep)
        is_list = 0

    if is_String(newpath):
        newpaths = newpath.split(sep)
    elif not is_List(newpath) and not is_Tuple(newpath):
        newpaths = [ newpath ]  # might be a Dir
    else:
        newpaths = newpath

    if canonicalize:
        newpaths=list(map(canonicalize, newpaths))

    if not delete_existing:
        # First uniquify the old paths, making sure to 
        # preserve the first instance (in Unix/Linux,
        # the first one wins), and remembering them in normpaths.
        # Then insert the new paths at the head of the list
        # if they're not already in the normpaths list.
        result = []
        normpaths = []
        for path in paths:
            if not path:
                continue
            normpath = os.path.normpath(os.path.normcase(path))
            if normpath not in normpaths:
                result.append(path)
                normpaths.append(normpath)
        newpaths.reverse()      # since we're inserting at the head
        for path in newpaths:
            if not path:
                continue
            normpath = os.path.normpath(os.path.normcase(path))
            if normpath not in normpaths:
                result.insert(0, path)
                normpaths.append(normpath)
        paths = result

    else:
        newpaths = newpaths + paths # prepend new paths

        normpaths = []
        paths = []
        # now we add them only if they are unique
        for path in newpaths:
            normpath = os.path.normpath(os.path.normcase(path))
            if path and not normpath in normpaths:
                paths.append(path)
                normpaths.append(normpath)

    if is_list:
        return paths
    else:
        return sep.join(paths)

def AppendPath(oldpath, newpath, sep = os.pathsep, 
               delete_existing=1, canonicalize=None):
    """This appends new path elements to the given old path.  Will
    only add any particular path once (leaving the last one it
    encounters and ignoring the rest, to preserve path order), and
    will os.path.normpath and os.path.normcase all paths to help
    assure this.  This can also handle the case where the given old
    path variable is a list instead of a string, in which case a list
    will be returned instead of a string.

    Example:
      Old Path: "/foo/bar:/foo"
      New Path: "/biz/boom:/foo"
      Result:   "/foo/bar:/biz/boom:/foo"

    If delete_existing is 0, then adding a path that exists
    will not move it to the end; it will stay where it is in the list.

    If canonicalize is not None, it is applied to each element of 
    newpath before use.
    """

    orig = oldpath
    is_list = 1
    paths = orig
    if not is_List(orig) and not is_Tuple(orig):
        paths = paths.split(sep)
        is_list = 0

    if is_String(newpath):
        newpaths = newpath.split(sep)
    elif not is_List(newpath) and not is_Tuple(newpath):
        newpaths = [ newpath ]  # might be a Dir
    else:
        newpaths = newpath

    if canonicalize:
        newpaths=list(map(canonicalize, newpaths))

    if not delete_existing:
        # add old paths to result, then
        # add new paths if not already present
        # (I thought about using a dict for normpaths for speed,
        # but it's not clear hashing the strings would be faster
        # than linear searching these typically short lists.)
        result = []
        normpaths = []
        for path in paths:
            if not path:
                continue
            result.append(path)
            normpaths.append(os.path.normpath(os.path.normcase(path)))
        for path in newpaths:
            if not path:
                continue
            normpath = os.path.normpath(os.path.normcase(path))
            if normpath not in normpaths:
                result.append(path)
                normpaths.append(normpath)
        paths = result
    else:
        # start w/ new paths, add old ones if not present,
        # then reverse.
        newpaths = paths + newpaths # append new paths
        newpaths.reverse()

        normpaths = []
        paths = []
        # now we add them only if they are unique
        for path in newpaths:
            normpath = os.path.normpath(os.path.normcase(path))
            if path and not normpath in normpaths:
                paths.append(path)
                normpaths.append(normpath)
        paths.reverse()

    if is_list:
        return paths
    else:
        return sep.join(paths)

if sys.platform == 'cygwin':
    def get_native_path(path):
        """Transforms an absolute path into a native path for the system.  In
        Cygwin, this converts from a Cygwin path to a Windows one."""
        return os.popen('cygpath -w ' + path).read().replace('\n', '')
else:
    def get_native_path(path):
        """Transforms an absolute path into a native path for the system.
        Non-Cygwin version, just leave the path alone."""
        return path

display = DisplayEngine()

def Split(arg):
    if is_List(arg) or is_Tuple(arg):
        return arg
    elif is_String(arg):
        return arg.split()
    else:
        return [arg]

class CLVar(UserList):
    """A class for command-line construction variables.

    This is a list that uses Split() to split an initial string along
    white-space arguments, and similarly to split any strings that get
    added.  This allows us to Do the Right Thing with Append() and
    Prepend() (as well as straight Python foo = env['VAR'] + 'arg1
    arg2') regardless of whether a user adds a list or a string to a
    command-line construction variable.
    """
    def __init__(self, seq = []):
        UserList.__init__(self, Split(seq))
    def __add__(self, other):
        return UserList.__add__(self, CLVar(other))
    def __radd__(self, other):
        return UserList.__radd__(self, CLVar(other))
    def __coerce__(self, other):
        return (self, CLVar(other))
    def __str__(self):
        return ' '.join(self.data)

# A dictionary that preserves the order in which items are added.
# Submitted by David Benjamin to ActiveState's Python Cookbook web site:
#     http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/107747
# Including fixes/enhancements from the follow-on discussions.
class OrderedDict(UserDict):
    def __init__(self, dict = None):
        self._keys = []
        UserDict.__init__(self, dict)

    def __delitem__(self, key):
        UserDict.__delitem__(self, key)
        self._keys.remove(key)

    def __setitem__(self, key, item):
        UserDict.__setitem__(self, key, item)
        if key not in self._keys: self._keys.append(key)

    def clear(self):
        UserDict.clear(self)
        self._keys = []

    def copy(self):
        dict = OrderedDict()
        dict.update(self)
        return dict

    def items(self):
        return list(zip(self._keys, list(self.values())))

    def keys(self):
        return self._keys[:]

    def popitem(self):
        try:
            key = self._keys[-1]
        except IndexError:
            raise KeyError('dictionary is empty')

        val = self[key]
        del self[key]

        return (key, val)

    def setdefault(self, key, failobj = None):
        UserDict.setdefault(self, key, failobj)
        if key not in self._keys: self._keys.append(key)

    def update(self, dict):
        for (key, val) in dict.items():
            self.__setitem__(key, val)

    def values(self):
        return list(map(self.get, self._keys))

class Selector(OrderedDict):
    """A callable ordered dictionary that maps file suffixes to
    dictionary values.  We preserve the order in which items are added
    so that get_suffix() calls always return the first suffix added."""
    def __call__(self, env, source, ext=None):
        if ext is None:
            try:
                ext = source[0].suffix
            except IndexError:
                ext = ""
        try:
            return self[ext]
        except KeyError:
            # Try to perform Environment substitution on the keys of
            # the dictionary before giving up.
            s_dict = {}
            for (k,v) in self.items():
                if k is not None:
                    s_k = env.subst(k)
                    if s_k in s_dict:
                        # We only raise an error when variables point
                        # to the same suffix.  If one suffix is literal
                        # and a variable suffix contains this literal,
                        # the literal wins and we don't raise an error.
                        raise KeyError(s_dict[s_k][0], k, s_k)
                    s_dict[s_k] = (k,v)
            try:
                return s_dict[ext][1]
            except KeyError:
                try:
                    return self[None]
                except KeyError:
                    return None


if sys.platform == 'cygwin':
    # On Cygwin, os.path.normcase() lies, so just report back the
    # fact that the underlying Windows OS is case-insensitive.
    def case_sensitive_suffixes(s1, s2):
        return 0
else:
    def case_sensitive_suffixes(s1, s2):
        return (os.path.normcase(s1) != os.path.normcase(s2))

def adjustixes(fname, pre, suf, ensure_suffix=False):
    if pre:
        path, fn = os.path.split(os.path.normpath(fname))
        if fn[:len(pre)] != pre:
            fname = os.path.join(path, pre + fn)
    # Only append a suffix if the suffix we're going to add isn't already
    # there, and if either we've been asked to ensure the specific suffix
    # is present or there's no suffix on it at all.
    if suf and fname[-len(suf):] != suf and \
       (ensure_suffix or not splitext(fname)[1]):
            fname = fname + suf
    return fname



# From Tim Peters,
# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560
# ASPN: Python Cookbook: Remove duplicates from a sequence
# (Also in the printed Python Cookbook.)

def unique(s):
    """Return a list of the elements in s, but without duplicates.

    For example, unique([1,2,3,1,2,3]) is some permutation of [1,2,3],
    unique("abcabc") some permutation of ["a", "b", "c"], and
    unique(([1, 2], [2, 3], [1, 2])) some permutation of
    [[2, 3], [1, 2]].

    For best speed, all sequence elements should be hashable.  Then
    unique() will usually work in linear time.

    If not possible, the sequence elements should enjoy a total
    ordering, and if list(s).sort() doesn't raise TypeError it's
    assumed that they do enjoy a total ordering.  Then unique() will
    usually work in O(N*log2(N)) time.

    If that's not possible either, the sequence elements must support
    equality-testing.  Then unique() will usually work in quadratic
    time.
    """

    n = len(s)
    if n == 0:
        return []

    # Try using a dict first, as that's the fastest and will usually
    # work.  If it doesn't work, it will usually fail quickly, so it
    # usually doesn't cost much to *try* it.  It requires that all the
    # sequence elements be hashable, and support equality comparison.
    u = {}
    try:
        for x in s:
            u[x] = 1
    except TypeError:
        pass    # move on to the next method
    else:
        return list(u.keys())
    del u

    # We can't hash all the elements.  Second fastest is to sort,
    # which brings the equal elements together; then duplicates are
    # easy to weed out in a single pass.
    # NOTE:  Python's list.sort() was designed to be efficient in the
    # presence of many duplicate elements.  This isn't true of all
    # sort functions in all languages or libraries, so this approach
    # is more effective in Python than it may be elsewhere.
    try:
        t = sorted(s)
    except TypeError:
        pass    # move on to the next method
    else:
        assert n > 0
        last = t[0]
        lasti = i = 1
        while i < n:
            if t[i] != last:
                t[lasti] = last = t[i]
                lasti = lasti + 1
            i = i + 1
        return t[:lasti]
    del t

    # Brute force is all that's left.
    u = []
    for x in s:
        if x not in u:
            u.append(x)
    return u



# From Alex Martelli,
# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560
# ASPN: Python Cookbook: Remove duplicates from a sequence
# First comment, dated 2001/10/13.
# (Also in the printed Python Cookbook.)

def uniquer(seq, idfun=None):
    if idfun is None:
        def idfun(x): return x
    seen = {}
    result = []
    for item in seq:
        marker = idfun(item)
        # in old Python versions:
        # if seen.has_key(marker)
        # but in new ones:
        if marker in seen: continue
        seen[marker] = 1
        result.append(item)
    return result

# A more efficient implementation of Alex's uniquer(), this avoids the
# idfun() argument and function-call overhead by assuming that all
# items in the sequence are hashable.

def uniquer_hashables(seq):
    seen = {}
    result = []
    for item in seq:
        #if not item in seen:
        if item not in seen:
            seen[item] = 1
            result.append(item)
    return result



# Much of the logic here was originally based on recipe 4.9 from the
# Python CookBook, but we had to dumb it way down for Python 1.5.2.
class LogicalLines(object):

    def __init__(self, fileobj):
        self.fileobj = fileobj

    def readline(self):
        result = []
        while True:
            line = self.fileobj.readline()
            if not line:
                break
            if line[-2:] == '\\\n':
                result.append(line[:-2])
            else:
                result.append(line)
                break
        return ''.join(result)

    def readlines(self):
        result = []
        while True:
            line = self.readline()
            if not line:
                break
            result.append(line)
        return result



class UniqueList(UserList):
    def __init__(self, seq = []):
        UserList.__init__(self, seq)
        self.unique = True
    def __make_unique(self):
        if not self.unique:
            self.data = uniquer_hashables(self.data)
            self.unique = True
    def __lt__(self, other):
        self.__make_unique()
        return UserList.__lt__(self, other)
    def __le__(self, other):
        self.__make_unique()
        return UserList.__le__(self, other)
    def __eq__(self, other):
        self.__make_unique()
        return UserList.__eq__(self, other)
    def __ne__(self, other):
        self.__make_unique()
        return UserList.__ne__(self, other)
    def __gt__(self, other):
        self.__make_unique()
        return UserList.__gt__(self, other)
    def __ge__(self, other):
        self.__make_unique()
        return UserList.__ge__(self, other)
    def __cmp__(self, other):
        self.__make_unique()
        return UserList.__cmp__(self, other)
    def __len__(self):
        self.__make_unique()
        return UserList.__len__(self)
    def __getitem__(self, i):
        self.__make_unique()
        return UserList.__getitem__(self, i)
    def __setitem__(self, i, item):
        UserList.__setitem__(self, i, item)
        self.unique = False
    def __getslice__(self, i, j):
        self.__make_unique()
        return UserList.__getslice__(self, i, j)
    def __setslice__(self, i, j, other):
        UserList.__setslice__(self, i, j, other)
        self.unique = False
    def __add__(self, other):
        result = UserList.__add__(self, other)
        result.unique = False
        return result
    def __radd__(self, other):
        result = UserList.__radd__(self, other)
        result.unique = False
        return result
    def __iadd__(self, other):
        result = UserList.__iadd__(self, other)
        result.unique = False
        return result
    def __mul__(self, other):
        result = UserList.__mul__(self, other)
        result.unique = False
        return result
    def __rmul__(self, other):
        result = UserList.__rmul__(self, other)
        result.unique = False
        return result
    def __imul__(self, other):
        result = UserList.__imul__(self, other)
        result.unique = False
        return result
    def append(self, item):
        UserList.append(self, item)
        self.unique = False
    def insert(self, i):
        UserList.insert(self, i)
        self.unique = False
    def count(self, item):
        self.__make_unique()
        return UserList.count(self, item)
    def index(self, item):
        self.__make_unique()
        return UserList.index(self, item)
    def reverse(self):
        self.__make_unique()
        UserList.reverse(self)
    def sort(self, *args, **kwds):
        self.__make_unique()
        return UserList.sort(self, *args, **kwds)
    def extend(self, other):
        UserList.extend(self, other)
        self.unique = False


class Unbuffered(object):
    """
    A proxy class that wraps a file object, flushing after every write,
    and delegating everything else to the wrapped object.
    """
    def __init__(self, file):
        self.file = file
        self.softspace = 0  ## backward compatibility; not supported in Py3k
    def write(self, arg):
        try:
            self.file.write(arg)
            self.file.flush()
        except IOError:
            # Stdout might be connected to a pipe that has been closed
            # by now. The most likely reason for the pipe being closed
            # is that the user has press ctrl-c. It this is the case,
            # then SCons is currently shutdown. We therefore ignore
            # IOError's here so that SCons can continue and shutdown
            # properly so that the .sconsign is correctly written
            # before SCons exits.
            pass
    def __getattr__(self, attr):
        return getattr(self.file, attr)

def make_path_relative(path):
    """ makes an absolute path name to a relative pathname.
    """
    if os.path.isabs(path):
        drive_s,path = os.path.splitdrive(path)

        import re
        if not drive_s:
            path=re.compile("/*(.*)").findall(path)[0]
        else:
            path=path[1:]

    assert( not os.path.isabs( path ) ), path
    return path



# The original idea for AddMethod() and RenameFunction() come from the
# following post to the ActiveState Python Cookbook:
#
#	ASPN: Python Cookbook : Install bound methods in an instance
#	http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/223613
#
# That code was a little fragile, though, so the following changes
# have been wrung on it:
#
# * Switched the installmethod() "object" and "function" arguments,
#   so the order reflects that the left-hand side is the thing being
#   "assigned to" and the right-hand side is the value being assigned.
#
# * Changed explicit type-checking to the "try: klass = object.__class__"
#   block in installmethod() below so that it still works with the
#   old-style classes that SCons uses.
#
# * Replaced the by-hand creation of methods and functions with use of
#   the "new" module, as alluded to in Alex Martelli's response to the
#   following Cookbook post:
#
#	ASPN: Python Cookbook : Dynamically added methods to a class
#	http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/81732

def AddMethod(obj, function, name=None):
    """
    Adds either a bound method to an instance or an unbound method to
    a class. If name is ommited the name of the specified function
    is used by default.
    Example:
      a = A()
      def f(self, x, y):
        self.z = x + y
      AddMethod(f, A, "add")
      a.add(2, 4)
      print a.z
      AddMethod(lambda self, i: self.l[i], a, "listIndex")
      print a.listIndex(5)
    """
    if name is None:
        name = function.func_name
    else:
        function = RenameFunction(function, name)

    if hasattr(obj, '__class__') and obj.__class__ is not type:
        # "obj" is an instance, so it gets a bound method.
        setattr(obj, name, MethodType(function, obj, obj.__class__))
    else:
        # "obj" is a class, so it gets an unbound method.
        setattr(obj, name, MethodType(function, None, obj))

def RenameFunction(function, name):
    """
    Returns a function identical to the specified function, but with
    the specified name.
    """
    return FunctionType(function.func_code,
                        function.func_globals,
                        name,
                        function.func_defaults)


md5 = False
def MD5signature(s):
    return str(s)

def MD5filesignature(fname, chunksize=65536):
    f = open(fname, "rb")
    result = f.read()
    f.close()
    return result

try:
    import hashlib
except ImportError:
    pass
else:
    if hasattr(hashlib, 'md5'):
        md5 = True
        def MD5signature(s):
            m = hashlib.md5()
            m.update(str(s))
            return m.hexdigest()

        def MD5filesignature(fname, chunksize=65536):
            m = hashlib.md5()
            f = open(fname, "rb")
            while True:
                blck = f.read(chunksize)
                if not blck:
                    break
                m.update(str(blck))
            f.close()
            return m.hexdigest()
            
def MD5collect(signatures):
    """
    Collects a list of signatures into an aggregate signature.

    signatures - a list of signatures
    returns - the aggregate signature
    """
    if len(signatures) == 1:
        return signatures[0]
    else:
        return MD5signature(', '.join(signatures))



def silent_intern(x):
    """
    Perform sys.intern() on the passed argument and return the result.
    If the input is ineligible (e.g. a unicode string) the original argument is
    returned and no exception is thrown.
    """
    try:
        return sys.intern(x)
    except TypeError:
        return x



# From Dinu C. Gherman,
# Python Cookbook, second edition, recipe 6.17, p. 277.
# Also:
# http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/68205
# ASPN: Python Cookbook: Null Object Design Pattern

#TODO??? class Null(object):
class Null(object):
    """ Null objects always and reliably "do nothing." """
    def __new__(cls, *args, **kwargs):
        if not '_instance' in vars(cls):
            cls._instance = super(Null, cls).__new__(cls, *args, **kwargs)
        return cls._instance
    def __init__(self, *args, **kwargs):
        pass
    def __call__(self, *args, **kwargs):
        return self
    def __repr__(self):
        return "Null(0x%08X)" % id(self)
    def __nonzero__(self):
        return False
    def __getattr__(self, name):
        return self
    def __setattr__(self, name, value):
        return self
    def __delattr__(self, name):
        return self

class NullSeq(Null):
    def __len__(self):
        return 0
    def __iter__(self):
        return iter(())
    def __getitem__(self, i):
        return self
    def __delitem__(self, i):
        return self
    def __setitem__(self, i, v):
        return self


del __revision__

# Local Variables:
# tab-width:4
# indent-tabs-mode:nil
# End:
# vim: set expandtab tabstop=4 shiftwidth=4: