[issue20742] 2to3 zip fixer doesn't fix for loops.

[Irit Katriel]

Change by Irit Katriel :


--
resolution:  -> duplicate
stage:  -> resolved
status: open -> closed
superseder:  -> Close 2to3 issues and list them here

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[issue20742] 2to3 zip fixer doesn't fix for loops.

[RobertG]

RobertG added the comment:

As far as a non contrived example, see http://bugs.python.org/issue21628, which 
was marked as a duplicate of this bug.

This bug is the main thing preventing me from using 2to3, so I think it is a 
real issue.

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[issue20742] 2to3 zip fixer doesn't fix for loops.

[Berker Peksag]

Changes by Berker Peksag berker.pek...@gmail.com:


--
nosy: +RobertG, benjamin.peterson
versions: +Python 2.7, Python 3.4, Python 3.5 -Python 3.2

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[issue20742] 2to3 zip fixer doesn't fix for loops.

[David Jones]

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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[issue20742] 2to3 zip fixer doesn't fix for loops.

[Peter Otten]

Peter Otten added the comment:

Hm, I would expect that in 99 times out of 100 the extra list(...) would be 
removed in a manual step following the automated conversion.

I'd really like to see the non-contrived example with a justified use of this 
evil side effect ;)

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nosy: +peter.otten

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