-
-
Notifications
You must be signed in to change notification settings - Fork 31.7k
/
Copy pathtest_generators.py
2689 lines (2236 loc) · 70.7 KB
/
test_generators.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
import copy
import gc
import pickle
import sys
import doctest
import unittest
import weakref
import inspect
import types
from test import support
try:
import _testcapi
except ImportError:
_testcapi = None
# This tests to make sure that if a SIGINT arrives just before we send into a
# yield from chain, the KeyboardInterrupt is raised in the innermost
# generator (see bpo-30039).
@unittest.skipUnless(_testcapi is not None and
hasattr(_testcapi, "raise_SIGINT_then_send_None"),
"needs _testcapi.raise_SIGINT_then_send_None")
class SignalAndYieldFromTest(unittest.TestCase):
def generator1(self):
return (yield from self.generator2())
def generator2(self):
try:
yield
except KeyboardInterrupt:
return "PASSED"
else:
return "FAILED"
def test_raise_and_yield_from(self):
gen = self.generator1()
gen.send(None)
try:
_testcapi.raise_SIGINT_then_send_None(gen)
except BaseException as _exc:
exc = _exc
self.assertIs(type(exc), StopIteration)
self.assertEqual(exc.value, "PASSED")
class FinalizationTest(unittest.TestCase):
def test_frame_resurrect(self):
# A generator frame can be resurrected by a generator's finalization.
def gen():
nonlocal frame
try:
yield
finally:
frame = sys._getframe()
g = gen()
wr = weakref.ref(g)
next(g)
del g
support.gc_collect()
self.assertIs(wr(), None)
self.assertTrue(frame)
del frame
support.gc_collect()
def test_refcycle(self):
# A generator caught in a refcycle gets finalized anyway.
old_garbage = gc.garbage[:]
finalized = False
def gen():
nonlocal finalized
try:
g = yield
yield 1
finally:
finalized = True
g = gen()
next(g)
g.send(g)
self.assertGreater(sys.getrefcount(g), 2)
self.assertFalse(finalized)
del g
support.gc_collect()
self.assertTrue(finalized)
self.assertEqual(gc.garbage, old_garbage)
def test_lambda_generator(self):
# bpo-23192, gh-119897: Test that a lambda returning a generator behaves
# like the equivalent function
f = lambda: (yield 1)
self.assertIsInstance(f(), types.GeneratorType)
self.assertEqual(next(f()), 1)
def g(): return (yield 1)
# test 'yield from'
f2 = lambda: (yield from g())
def g2(): return (yield from g())
f3 = lambda: (yield from f())
def g3(): return (yield from f())
for gen_fun in (f, g, f2, g2, f3, g3):
gen = gen_fun()
self.assertEqual(next(gen), 1)
with self.assertRaises(StopIteration) as cm:
gen.send(2)
self.assertEqual(cm.exception.value, 2)
class GeneratorTest(unittest.TestCase):
def test_name(self):
def func():
yield 1
# check generator names
gen = func()
self.assertEqual(gen.__name__, "func")
self.assertEqual(gen.__qualname__,
"GeneratorTest.test_name.<locals>.func")
# modify generator names
gen.__name__ = "name"
gen.__qualname__ = "qualname"
self.assertEqual(gen.__name__, "name")
self.assertEqual(gen.__qualname__, "qualname")
# generator names must be a string and cannot be deleted
self.assertRaises(TypeError, setattr, gen, '__name__', 123)
self.assertRaises(TypeError, setattr, gen, '__qualname__', 123)
self.assertRaises(TypeError, delattr, gen, '__name__')
self.assertRaises(TypeError, delattr, gen, '__qualname__')
# modify names of the function creating the generator
func.__qualname__ = "func_qualname"
func.__name__ = "func_name"
gen = func()
self.assertEqual(gen.__name__, "func_name")
self.assertEqual(gen.__qualname__, "func_qualname")
# unnamed generator
gen = (x for x in range(10))
self.assertEqual(gen.__name__,
"<genexpr>")
self.assertEqual(gen.__qualname__,
"GeneratorTest.test_name.<locals>.<genexpr>")
def test_copy(self):
def f():
yield 1
g = f()
with self.assertRaises(TypeError):
copy.copy(g)
def test_pickle(self):
def f():
yield 1
g = f()
for proto in range(pickle.HIGHEST_PROTOCOL + 1):
with self.assertRaises((TypeError, pickle.PicklingError)):
pickle.dumps(g, proto)
def test_send_non_none_to_new_gen(self):
def f():
yield 1
g = f()
with self.assertRaises(TypeError):
g.send(0)
self.assertEqual(next(g), 1)
def test_handle_frame_object_in_creation(self):
#Attempt to expose partially constructed frames
#See https://github.com/python/cpython/issues/94262
def cb(*args):
inspect.stack()
def gen():
yield 1
thresholds = gc.get_threshold()
gc.callbacks.append(cb)
gc.set_threshold(1, 0, 0)
try:
gen()
finally:
gc.set_threshold(*thresholds)
gc.callbacks.pop()
class Sneaky:
def __del__(self):
inspect.stack()
sneaky = Sneaky()
sneaky._s = Sneaky()
sneaky._s._s = sneaky
gc.set_threshold(1, 0, 0)
try:
del sneaky
gen()
finally:
gc.set_threshold(*thresholds)
def test_ag_frame_f_back(self):
async def f():
yield
ag = f()
self.assertIsNone(ag.ag_frame.f_back)
def test_cr_frame_f_back(self):
async def f():
pass
cr = f()
self.assertIsNone(cr.cr_frame.f_back)
cr.close() # Suppress RuntimeWarning.
def test_gi_frame_f_back(self):
def f():
yield
gi = f()
self.assertIsNone(gi.gi_frame.f_back)
def test_issue103488(self):
def gen_raises():
yield
raise ValueError()
def loop():
try:
for _ in gen_raises():
if True is False:
return
except ValueError:
pass
#This should not raise
loop()
class ModifyUnderlyingIterableTest(unittest.TestCase):
iterables = [
range(0),
range(20),
[1, 2, 3],
(2,),
{13, 48, 211},
frozenset((15, 8, 6)),
{1: 2, 3: 4},
]
non_iterables = [
None,
42,
3.0,
2j,
]
def genexpr(self):
return (x for x in range(10))
def genfunc(self):
def gen(it):
for x in it:
yield x
return gen(range(10))
def process_tests(self, get_generator):
for obj in self.iterables:
g_obj = get_generator(obj)
with self.subTest(g_obj=g_obj, obj=obj):
self.assertListEqual(list(g_obj), list(obj))
g_iter = get_generator(iter(obj))
with self.subTest(g_iter=g_iter, obj=obj):
self.assertListEqual(list(g_iter), list(obj))
err_regex = "'.*' object is not iterable"
for obj in self.non_iterables:
g_obj = get_generator(obj)
with self.subTest(g_obj=g_obj):
self.assertRaisesRegex(TypeError, err_regex, list, g_obj)
def test_modify_f_locals(self):
def modify_f_locals(g, local, obj):
g.gi_frame.f_locals[local] = obj
return g
def get_generator_genexpr(obj):
return modify_f_locals(self.genexpr(), '.0', obj)
def get_generator_genfunc(obj):
return modify_f_locals(self.genfunc(), 'it', obj)
self.process_tests(get_generator_genexpr)
self.process_tests(get_generator_genfunc)
def test_new_gen_from_gi_code(self):
def new_gen_from_gi_code(g, obj):
generator_func = types.FunctionType(g.gi_code, {})
return generator_func(obj)
def get_generator_genexpr(obj):
return new_gen_from_gi_code(self.genexpr(), obj)
def get_generator_genfunc(obj):
return new_gen_from_gi_code(self.genfunc(), obj)
self.process_tests(get_generator_genexpr)
self.process_tests(get_generator_genfunc)
class ExceptionTest(unittest.TestCase):
# Tests for the issue #23353: check that the currently handled exception
# is correctly saved/restored in PyEval_EvalFrameEx().
def test_except_throw(self):
def store_raise_exc_generator():
try:
self.assertIsNone(sys.exception())
yield
except Exception as exc:
# exception raised by gen.throw(exc)
self.assertIsInstance(sys.exception(), ValueError)
self.assertIsNone(exc.__context__)
yield
# ensure that the exception is not lost
self.assertIsInstance(sys.exception(), ValueError)
yield
# we should be able to raise back the ValueError
raise
make = store_raise_exc_generator()
next(make)
try:
raise ValueError()
except Exception as exc:
try:
make.throw(exc)
except Exception:
pass
next(make)
with self.assertRaises(ValueError) as cm:
next(make)
self.assertIsNone(cm.exception.__context__)
self.assertIsNone(sys.exception())
def test_except_next(self):
def gen():
self.assertIsInstance(sys.exception(), ValueError)
yield "done"
g = gen()
try:
raise ValueError
except Exception:
self.assertEqual(next(g), "done")
self.assertIsNone(sys.exception())
def test_except_gen_except(self):
def gen():
try:
self.assertIsNone(sys.exception())
yield
# we are called from "except ValueError:", TypeError must
# inherit ValueError in its context
raise TypeError()
except TypeError as exc:
self.assertIsInstance(sys.exception(), TypeError)
self.assertEqual(type(exc.__context__), ValueError)
# here we are still called from the "except ValueError:"
self.assertIsInstance(sys.exception(), ValueError)
yield
self.assertIsNone(sys.exception())
yield "done"
g = gen()
next(g)
try:
raise ValueError
except Exception:
next(g)
self.assertEqual(next(g), "done")
self.assertIsNone(sys.exception())
def test_nested_gen_except_loop(self):
def gen():
for i in range(100):
self.assertIsInstance(sys.exception(), TypeError)
yield "doing"
def outer():
try:
raise TypeError
except:
for x in gen():
yield x
try:
raise ValueError
except Exception:
for x in outer():
self.assertEqual(x, "doing")
self.assertEqual(sys.exception(), None)
def test_except_throw_exception_context(self):
def gen():
try:
try:
self.assertIsNone(sys.exception())
yield
except ValueError:
# we are called from "except ValueError:"
self.assertIsInstance(sys.exception(), ValueError)
raise TypeError()
except Exception as exc:
self.assertIsInstance(sys.exception(), TypeError)
self.assertEqual(type(exc.__context__), ValueError)
# we are still called from "except ValueError:"
self.assertIsInstance(sys.exception(), ValueError)
yield
self.assertIsNone(sys.exception())
yield "done"
g = gen()
next(g)
try:
raise ValueError
except Exception as exc:
g.throw(exc)
self.assertEqual(next(g), "done")
self.assertIsNone(sys.exception())
def test_except_throw_bad_exception(self):
class E(Exception):
def __new__(cls, *args, **kwargs):
return cls
def boring_generator():
yield
gen = boring_generator()
err_msg = 'should have returned an instance of BaseException'
with self.assertRaisesRegex(TypeError, err_msg):
gen.throw(E)
self.assertRaises(StopIteration, next, gen)
def generator():
with self.assertRaisesRegex(TypeError, err_msg):
yield
gen = generator()
next(gen)
with self.assertRaises(StopIteration):
gen.throw(E)
def test_gen_3_arg_deprecation_warning(self):
def g():
yield 42
gen = g()
with self.assertWarns(DeprecationWarning):
with self.assertRaises(TypeError):
gen.throw(TypeError, TypeError(24), None)
def test_stopiteration_error(self):
# See also PEP 479.
def gen():
raise StopIteration
yield
with self.assertRaisesRegex(RuntimeError, 'raised StopIteration'):
next(gen())
def test_tutorial_stopiteration(self):
# Raise StopIteration" stops the generator too:
def f():
yield 1
raise StopIteration
yield 2 # never reached
g = f()
self.assertEqual(next(g), 1)
with self.assertRaisesRegex(RuntimeError, 'raised StopIteration'):
next(g)
def test_return_tuple(self):
def g():
return (yield 1)
gen = g()
self.assertEqual(next(gen), 1)
with self.assertRaises(StopIteration) as cm:
gen.send((2,))
self.assertEqual(cm.exception.value, (2,))
def test_return_stopiteration(self):
def g():
return (yield 1)
gen = g()
self.assertEqual(next(gen), 1)
with self.assertRaises(StopIteration) as cm:
gen.send(StopIteration(2))
self.assertIsInstance(cm.exception.value, StopIteration)
self.assertEqual(cm.exception.value.value, 2)
class GeneratorCloseTest(unittest.TestCase):
def test_close_no_return_value(self):
def f():
yield
gen = f()
gen.send(None)
self.assertIsNone(gen.close())
def test_close_return_value(self):
def f():
try:
yield
# close() raises GeneratorExit here, which is caught
except GeneratorExit:
return 0
gen = f()
gen.send(None)
self.assertEqual(gen.close(), 0)
def test_close_not_catching_exit(self):
def f():
yield
# close() raises GeneratorExit here, which isn't caught and
# therefore propagates -- no return value
return 0
gen = f()
gen.send(None)
self.assertIsNone(gen.close())
def test_close_not_started(self):
def f():
try:
yield
except GeneratorExit:
return 0
gen = f()
self.assertIsNone(gen.close())
def test_close_exhausted(self):
def f():
try:
yield
except GeneratorExit:
return 0
gen = f()
next(gen)
with self.assertRaises(StopIteration):
next(gen)
self.assertIsNone(gen.close())
def test_close_closed(self):
def f():
try:
yield
except GeneratorExit:
return 0
gen = f()
gen.send(None)
self.assertEqual(gen.close(), 0)
self.assertIsNone(gen.close())
def test_close_raises(self):
def f():
try:
yield
except GeneratorExit:
pass
raise RuntimeError
gen = f()
gen.send(None)
with self.assertRaises(RuntimeError):
gen.close()
def test_close_releases_frame_locals(self):
# See gh-118272
class Foo:
pass
f = Foo()
f_wr = weakref.ref(f)
def genfn():
a = f
yield
g = genfn()
next(g)
del f
g.close()
support.gc_collect()
self.assertIsNone(f_wr())
class GeneratorThrowTest(unittest.TestCase):
def test_exception_context_with_yield(self):
def f():
try:
raise KeyError('a')
except Exception:
yield
gen = f()
gen.send(None)
with self.assertRaises(ValueError) as cm:
gen.throw(ValueError)
context = cm.exception.__context__
self.assertEqual((type(context), context.args), (KeyError, ('a',)))
def test_exception_context_with_yield_inside_generator(self):
# Check that the context is also available from inside the generator
# with yield, as opposed to outside.
def f():
try:
raise KeyError('a')
except Exception:
try:
yield
except Exception as exc:
self.assertEqual(type(exc), ValueError)
context = exc.__context__
self.assertEqual((type(context), context.args),
(KeyError, ('a',)))
yield 'b'
gen = f()
gen.send(None)
actual = gen.throw(ValueError)
# This ensures that the assertions inside were executed.
self.assertEqual(actual, 'b')
def test_exception_context_with_yield_from(self):
def f():
yield
def g():
try:
raise KeyError('a')
except Exception:
yield from f()
gen = g()
gen.send(None)
with self.assertRaises(ValueError) as cm:
gen.throw(ValueError)
context = cm.exception.__context__
self.assertEqual((type(context), context.args), (KeyError, ('a',)))
def test_exception_context_with_yield_from_with_context_cycle(self):
# Check trying to create an exception context cycle:
# https://bugs.python.org/issue40696
has_cycle = None
def f():
yield
def g(exc):
nonlocal has_cycle
try:
raise exc
except Exception:
try:
yield from f()
except Exception as exc:
has_cycle = (exc is exc.__context__)
yield
exc = KeyError('a')
gen = g(exc)
gen.send(None)
gen.throw(exc)
# This also distinguishes from the initial has_cycle=None.
self.assertEqual(has_cycle, False)
def test_throw_after_none_exc_type(self):
def g():
try:
raise KeyError
except KeyError:
pass
try:
yield
except Exception:
raise RuntimeError
gen = g()
gen.send(None)
with self.assertRaises(RuntimeError) as cm:
gen.throw(ValueError)
class GeneratorStackTraceTest(unittest.TestCase):
def check_stack_names(self, frame, expected):
names = []
while frame:
name = frame.f_code.co_name
# Stop checking frames when we get to our test helper.
if name.startswith('check_') or name.startswith('call_'):
break
names.append(name)
frame = frame.f_back
self.assertEqual(names, expected)
def check_yield_from_example(self, call_method):
def f():
self.check_stack_names(sys._getframe(), ['f', 'g'])
try:
yield
except Exception:
pass
self.check_stack_names(sys._getframe(), ['f', 'g'])
def g():
self.check_stack_names(sys._getframe(), ['g'])
yield from f()
self.check_stack_names(sys._getframe(), ['g'])
gen = g()
gen.send(None)
try:
call_method(gen)
except StopIteration:
pass
def test_send_with_yield_from(self):
def call_send(gen):
gen.send(None)
self.check_yield_from_example(call_send)
def test_throw_with_yield_from(self):
def call_throw(gen):
gen.throw(RuntimeError)
self.check_yield_from_example(call_throw)
class YieldFromTests(unittest.TestCase):
def test_generator_gi_yieldfrom(self):
def a():
self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_RUNNING)
self.assertIsNone(gen_b.gi_yieldfrom)
yield
self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_RUNNING)
self.assertIsNone(gen_b.gi_yieldfrom)
def b():
self.assertIsNone(gen_b.gi_yieldfrom)
yield from a()
self.assertIsNone(gen_b.gi_yieldfrom)
yield
self.assertIsNone(gen_b.gi_yieldfrom)
gen_b = b()
self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_CREATED)
self.assertIsNone(gen_b.gi_yieldfrom)
gen_b.send(None)
self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_SUSPENDED)
self.assertEqual(gen_b.gi_yieldfrom.gi_code.co_name, 'a')
gen_b.send(None)
self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_SUSPENDED)
self.assertIsNone(gen_b.gi_yieldfrom)
[] = gen_b # Exhaust generator
self.assertEqual(inspect.getgeneratorstate(gen_b), inspect.GEN_CLOSED)
self.assertIsNone(gen_b.gi_yieldfrom)
tutorial_tests = """
Let's try a simple generator:
>>> def f():
... yield 1
... yield 2
>>> for i in f():
... print(i)
1
2
>>> g = f()
>>> next(g)
1
>>> next(g)
2
"Falling off the end" stops the generator:
>>> next(g)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 2, in g
StopIteration
"return" also stops the generator:
>>> def f():
... yield 1
... return
... yield 2 # never reached
...
>>> g = f()
>>> next(g)
1
>>> next(g)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 3, in f
StopIteration
>>> next(g) # once stopped, can't be resumed
Traceback (most recent call last):
File "<stdin>", line 1, in ?
StopIteration
However, "return" and StopIteration are not exactly equivalent:
>>> def g1():
... try:
... return
... except:
... yield 1
...
>>> list(g1())
[]
>>> def g2():
... try:
... raise StopIteration
... except:
... yield 42
>>> print(list(g2()))
[42]
This may be surprising at first:
>>> def g3():
... try:
... return
... finally:
... yield 1
...
>>> list(g3())
[1]
Let's create an alternate range() function implemented as a generator:
>>> def yrange(n):
... for i in range(n):
... yield i
...
>>> list(yrange(5))
[0, 1, 2, 3, 4]
Generators always return to the most recent caller:
>>> def creator():
... r = yrange(5)
... print("creator", next(r))
... return r
...
>>> def caller():
... r = creator()
... for i in r:
... print("caller", i)
...
>>> caller()
creator 0
caller 1
caller 2
caller 3
caller 4
Generators can call other generators:
>>> def zrange(n):
... for i in yrange(n):
... yield i
...
>>> list(zrange(5))
[0, 1, 2, 3, 4]
"""
# The examples from PEP 255.
pep_tests = """
Specification: Yield
Restriction: A generator cannot be resumed while it is actively
running:
>>> def g():
... i = next(me)
... yield i
>>> me = g()
>>> next(me)
Traceback (most recent call last):
...
File "<string>", line 2, in g
ValueError: generator already executing
Specification: Return
Note that return isn't always equivalent to raising StopIteration: the
difference lies in how enclosing try/except constructs are treated.
For example,
>>> def f1():
... try:
... return
... except:
... yield 1
>>> print(list(f1()))
[]
because, as in any function, return simply exits, but
>>> def f2():
... try:
... raise StopIteration
... except:
... yield 42
>>> print(list(f2()))
[42]
because StopIteration is captured by a bare "except", as is any
exception.
Specification: Generators and Exception Propagation
>>> def f():
... return 1//0
>>> def g():
... yield f() # the zero division exception propagates
... yield 42 # and we'll never get here
>>> k = g()
>>> next(k)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 2, in g
File "<stdin>", line 2, in f
ZeroDivisionError: integer division or modulo by zero
>>> next(k) # and the generator cannot be resumed
Traceback (most recent call last):
File "<stdin>", line 1, in ?
StopIteration
>>>
Specification: Try/Except/Finally
>>> def f():
... try:
... yield 1
... try:
... yield 2