Patches item #1367711, was opened at 2005-11-27 21:18
Message generated for change (Comment added) made by loewis
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Category: Library (Lib)
Group: Python 2.5
Status: Open
Resolution: None
Priority: 3
Private: No
Submitted By: Wolfgang Langner (tds33)
Assigned to: Nobody/Anonymous (nobody)
Summary: Remove usage of UserDict from os.py
Initial Comment:
This patch removes UserDict usage from os.py.
It uses the new dict base class instead of UserDict.
Patch was generated against Revision 41544
of python subersion repository.
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>Comment By: Martin v. Löwis (loewis)
Date: 2006-11-20 00:01
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I believe the patch is wrong: it does not support setdefault() (which the
current code does).
It would be good if there were test cases for os.environ that made sure
all dictionary methods had the correct effect on the environment.
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Comment By: Wolfgang Langner (tds33)
Date: 2006-01-16 21:13
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The intend was to remove dependency on UserDict. Less
imports for a minimal python. If there are general problems
with the inheritence from dict than they should be
documented. I thought in future UserDict will gone.
I investigate this problems.
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Comment By: Armin Rigo (arigo)
Date: 2005-12-29 19:02
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Subclassing 'dict' to modify some behavior only works more
or less in CPython. There are a lot of (admitedly
convoluted) ways to get unexpected effects, where the
original methods are called instead of the overridden ones.
And it's not future-proof: if new methods are added to 'dict'
in the future, say a merge() similar to update() but not
replacing existing keys, then they will need to be added to
that subclass as well, or the method will misbehave. The
advantage of UserDict is to guard against all these problems.
For example, with the patch:
exec "global a; a=5" in os.environ
stores the key 'a' directly in os.environ, bypassing
the custom __setitem__(). With UserDict instead, we
get an explicit error. This is more a joke, but the
new-methods-appearing-later problem is more serious
IMHO.
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