[ python-Bugs-1517509 ] filter() implementation does not match docs

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Bugs item #1517509, was opened at 2006-07-05 09:09
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Category: Python Interpreter Core
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Submitted By: Collin Winter (collinwinter)
Assigned to: Nobody/Anonymous (nobody)
Summary: filter() implementation does not match docs

Initial Comment:
The docs for the built-in function filter() claim that
"filter(function, list) is equivalent to [item for item
in list if function(item)] if function is not None and
[item for item in list if item] if function is None".

>>> class infinite_str(str):
...     def __getitem__(self, index):
...         return "a"
...
>>> filter(None, infinite_str("1234"))
'aaaa'


Now, if we translate this to a listcomp according to
the docs:

>>> [x for x in infinite_str("1234") if x]

The listcomp version proceeds to chew up memory until
it exhausts the system resources or is killed by the user.

If the docs are to be believed, the filter() version
should do the same thing. 

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