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Why variable used in list comprehension available outside?

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pengyu.ut at gmail

May 2, 2012, 5:52 PM

Post #1 of 2 (170 views)
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Why variable used in list comprehension available outside?

Hi,

The following example demonstrates the variable 'v' used in the list
comprehension is accessible out site the list comprehension.

I think that 'v' should be strictly local. Does anybody know where
this behavior is documented and why it is designed this way?

~/linux/test/python/man/library/__buildin__/class/{/iteritems$ cat main1.py
#!/usr/bin/env python

d = {'one': 10, 'two': 20}

for k, v in d.iteritems():
print k, v
x=[2*v for v in [1, 2, 3]]
print x
print k, v
~/linux/test/python/man/library/__buildin__/class/{/iteritems$ ./main1.py
two 20
[2, 4, 6]
two 3
one 10
[2, 4, 6]
one 3

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Regards,
Peng
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python.list at tim

May 2, 2012, 6:23 PM

Post #2 of 2 (158 views)
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Re: Why variable used in list comprehension available outside? [In reply to]

On 05/02/12 19:52, Peng Yu wrote:
> The following example demonstrates the variable 'v' used in the
> list comprehension is accessible out site the list
> comprehension.

It did in Python 2.x but has been fixed in 3.x:

tim [at] bigbo:~$ python3
Python 3.1.3 (r313:86834, Nov 28 2010, 10:01:07)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> x = 42
>>> [x for x in range(10)]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> x
42
>>>

tim [at] bigbo:~$ python2.6
Python 2.6.6 (r266:84292, Dec 26 2010, 22:31:48)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> x = 42
>>> [x for x in range(10)]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> x
9
>>>

-tkc

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