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Life-time of temporary variables in list comprehensions

Diez B. Roggisch deets at nospam.web.de
Tue Oct 23 13:20:57 EDT 2007 
beginner schrieb:
> Hi All,
> 
> If I have a list comprehension:
> 
> ab=["A","B"]
> c = "ABC"
> [1.0 if c=='A' else c='B' for c in ab]
> print c
> 
>>> "B"
> 
> My test shows that if c is not defined before the list comprehension,
> it will be created in the list comprehension; if it is defined before
> the list comprehension, the value will be overwritten. In other words,
> temp variables are not local to list comprehensions.
> 
> My question is why is this and is there any way to make c local to
> list comp?


Unfortunately, not as such. They do leak their variable names.

But what you can do ist to create generator expressions (which don't 
leak) and put a list around them:

list(1.0 if c == 'A' else c="B" for c in ab)

See also

http://www.python.org/dev/peps/pep-0289/

Diez
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