[issue1617161] Instance methods compare equal when their self's are equal

[Alexander Belopolsky]

Alexander Belopolsky added the comment:

> the change was meant to unify
> the behavior of built-in and
> user method objects

I don't think it achieved that.  Consider:

>>> [].index == [].index
False

but
>>> UserList().index == UserList().index 
True

--
nosy: +belopolsky

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[issue1617161] Instance methods compare equal when their self's are equal

[Armin Rigo]

Armin Rigo <[EMAIL PROTECTED]> added the comment:

My mistake, you are right.  I forgot about one of the many types that
CPython uses internally for built-in methods.  Indeed:

>>> [].index == [].index
False
>>> [].__add__ == [].__add__
True

I can fix this so that the answer is True in all cases; alternatively,
considering Frank Niessink's original issue, we could bring this
discussion to python-dev and decide what the correct behavior should be
and implement it consistently for all method types.

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[issue1617161] Instance methods compare equal when their self's are equal

[Frank Niessink]

Frank Niessink <[EMAIL PROTECTED]> added the comment:

Just to reiterate the original bug report: the issue (for me) is that
currently (python 2.5):
>>> [].__add__  == [].__add__
True
>>> [].__add__  == [1].__add__
False

Or, using a non-builtin class:
>>> class C(object):
...   def __eq__(self, other):
... return False
...   def foo(self):
...  pass
...
>>> C().foo == C().foo
False
>>> class C(object):
...   def __eq__(self, other):
... return True
...   def foo(self):
... pass
...
>>> C().foo == C().foo
True

I think it makes little sense that the equality test for the instance
methods takes the equality of the instances into account. Imho, this
behaviour is inconsistent with the principle of no surprises. The
correct behaviour (again imho of course) is that instance methods only
compare equal to the same instance method of the same instance, where 
'same instance' is based on 'is' not on '=='.  

Cheers, Frank

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[issue1617161] Instance methods compare equal when their self's are equal

[Alexander Belopolsky]

Alexander Belopolsky <[EMAIL PROTECTED]> added the comment:

Armin,

I think this should be discussed on python-dev.  I don't understand your 
motivation for comparing methods of distinct but equal objects as equal.  
The callback argument on the other hand, is compelling.

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[issue1617161] Instance methods compare equal when their self's are equal

[Paul Pogonyshev]

Paul Pogonyshev <[EMAIL PROTECTED]> added the comment:

Since I'm not on python-dev, I'll mention here that the new behavior
makes no sense to me at all.  Which is best highlighted by Frank in
msg63414.

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nosy: +_doublep

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[issue1617161] Instance methods compare equal when their self's are equal

[Armin Rigo]

Armin Rigo <[EMAIL PROTECTED]> added the comment:

Attached patch for python trunk with tests.
It makes all three method types use the identity of their 'self'.

--
keywords: +patch
Added file: http://bugs.python.org/file9666/method_compare.diff

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[issue1617161] Instance methods compare equal when their self's are equal

[Mark Lawrence]

Mark Lawrence  added the comment:

msg84597 is ambiguous.  At first readng I thought it meant "the patches have 
been committed to trunk and py3k".  Second time I think it means "yes this is 
still a problem".  What is the status?

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[issue1617161] Instance methods compare equal when their self's are equal

[Alexander Belopolsky]

Alexander Belopolsky  added the comment:

I believe "Confirmed in trunk and py3k." means that the issue was verified to 
exist in trunk and py3k branches at the time of the message.

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[issue1617161] Instance methods compare equal when their self's are equal

[Terry J. Reedy]

Changes by Terry J. Reedy :


--
versions: +Python 3.2 -Python 2.7, Python 3.1

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[issue1617161] Instance methods compare equal when their self's are equal

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


--
nosy: +serhiy.storchaka
versions: +Python 3.4 -Python 3.2

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[issue1617161] Instance methods compare equal when their self's are equal

[Daniel Diniz]

Daniel Diniz  added the comment:

Confirmed in trunk and py3k.

--
nosy: +ajaksu2
stage:  -> patch review
type:  -> feature request
versions: +Python 2.7, Python 3.1 -Python 2.5

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