[issue27613] Empty iterator with fake __len__ is rendered as a single bracket ] when using json's iterencode
Terry J. Reedy
report at bugs.python.org
Sun Apr 23 16:45:03 EDT 2017
Terry J. Reedy added the comment:
Thank you Raymond. What I missed before is a) the OP's misnamed EmptyIterator is an iterable (possibly non-empty) but not an iterator, empty or otherwise, and b) a sequence __len__ that lies is just a bug. (So is a iterator that does not yield the contents of a collection.) A non-0 length(lst) is a promise that lst[0] exists. Depending on this is routine. If json.encoder line 296, 'for value in lst:' were replaced by the following, which should be equivalent,
for i in range(len(list)):
value = lst[i]
the encoding would die with IndexError.
The intention that buggy code should not cause a crash was met in this case.
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<http://bugs.python.org/issue27613>
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