[ python-Bugs-1204734 ] __getattribute__ documentation error?
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Bugs item #1204734, was opened at 2005-05-19 05:21
Message generated for change (Settings changed) made by gbrandl
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Category: Documentation
Group: None
Status: Closed
Resolution: Fixed
Priority: 5
Submitted By: John Eikenberry (zhar)
>Assigned to: Georg Brandl (gbrandl)
Summary: __getattribute__ documentation error?
Initial Comment:
>From http://www.python.org/dev/doc/devel/ref/new-style-attribute-access.html
"Called unconditionally to implement attribute accesses for instances of the class. If the class also defines __getattr__, it will never be called (unless called explicitly)."
But I'm not seeing this behaviour in python-2.3.5 and python-2.4.1 on Linux.
class A(object):
def __getattr__(self,key):
print '__getattr__',key
raise AttributeError,key
def __getattribute__(self,key):
print '__getattribute__',key
raise AttributeError,key
a = A()
a.foo
$ python test.py
__getattribute__ foo
__getattr__ foo
Traceback (most recent call last):
File "test.py", line 14, in ?
a.foo
File "test.py", line 7, in __getattr__
raise AttributeError(key)
AttributeError: foo
It seems to be calling __getattribute__ as it should, but then it falls back on __getattr__ even though the docs specifically say it shouldn't.
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Comment By: Georg Brandl (birkenfeld)
Date: 2005-07-02 10:30
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Checked in my patch as Doc/ref/ref3.tex r1.125, r1.121.2.4.
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Comment By: Georg Brandl (birkenfeld)
Date: 2005-06-04 10:03
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Attached a documentation patch, following Terry's wording.
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Comment By: Terry J. Reedy (tjreedy)
Date: 2005-05-26 17:42
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If I understand correctly, this revision of the consequent of the
second sentence (after ',') matches the implementation.
[If the class also defines __getattr__, ]
the latter will not be called unless __getattribute__ either calls it
explicitly or raises an AttributeError.
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Comment By: Guido van Rossum (gvanrossum)
Date: 2005-05-26 16:18
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The implementation works as expected.
The documentation is flawed.
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Comment By: John Eikenberry (zhar)
Date: 2005-05-26 15:52
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Terry, I started with a much longer subject but decided I
didn't want to overload it to much. Guess I went to far the
other way. I'll try to strike a better balance next time.
Thanks.
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Comment By: Terry J. Reedy (tjreedy)
Date: 2005-05-26 15:43
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John E: A general title like 'Documentation Error?' discourages
attention from people with the specialized knowledge needed to
answer such a question. I have taken the liberty of trying to
add '__getattribute__'. We'll see if the edit works when I, not the
OP, submits it.
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Comment By: Terry J. Reedy (tjreedy)
Date: 2005-05-26 15:33
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If the default __getattribute__ explicitly calls __getattr__ (but I
don't know which source file to check), then the second
sentence above *would* make some sense.
Guido (or deputy): what is your design intention?
Note: if the second sentence is kept, replacing 'it' with 'the latter'
would make it clearer. I first read 'it' as referring to
__getattribute__.
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Comment By: Armin Rigo (arigo)
Date: 2005-05-24 09:08
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I'll wait for an "authorized" confirmation, but so far I think that the current implementation is really how it is supposed to work. The method 'object.__getattribute__' must be there, given that it is a common technique to use it directly in overridden __getattribute__ implementations. As a consequence, __getattribute__ cannot completely shadow __getattr__, or __getattr__ would never be called.
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Comment By: John Eikenberry (zhar)
Date: 2005-05-23 18:43
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Please specify in the documentation whether this is how it
is supposed to work or whether this is a side-effect of the
implementation. To make explicit if you can write code
relying on this 'feature' and not have it break at some point.
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Comment By: Armin Rigo (arigo)
Date: 2005-05-23 14:28
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Indeed, the logic in typeobject.c is to call __getattribute__ and fall back on __getattr__ if the former raised an AttributeError. This is necessary because all objects have a __getattribute__, actually, as there is one in the 'object' base class. This let me think that the error is really in the documentation, which should mention this logic.
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