[New-bugs-announce] [issue20742] 2to3 zip fixer doesn't fix for loops.
David Jones
report at bugs.python.org
Sun Feb 23 12:11:47 CET 2014
New submission from David Jones:
Consider the following code:
for z in zip([1]):pass
2to3 does not convert the zip in this code to list(zip(...)); it does not change this code at all.
That can be an (obscure) bug because the zip in Python 2 has different semantics from the zip in Python 3.
The output of this program
from __future__ import print_function
S = []
def l(c):
for i in [0,1]:
S.append(c)
yield i
S.append(c.upper())
la = l('a')
lb = l('b')
for a,b in zip(la, lb):
S.append("#")
print(''.join(S))
is different in Python 2 and Python 3 (when converted with 2to3, which doesn't change the program).
In Python 2 the output is:
ababA##
In Python 3 the output is:
ab#ab#A
Obviously this example is somewhat contrived, but I have a non-contrived example involving decoding PNG images (if anyone is interested).
----------
components: 2to3 (2.x to 3.x conversion tool)
messages: 211989
nosy: drj
priority: normal
severity: normal
status: open
title: 2to3 zip fixer doesn't fix for loops.
type: behavior
versions: Python 3.2
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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue20742>
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