[ python-Bugs-1400227 ] 'is' does not work on methods

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Bugs item #1400227, was opened at 2006-01-09 10:04
Message generated for change (Comment added) made by mwh
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Category: Python Interpreter Core
Group: Python 2.4
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: Collin Winter (collinwinter)
>Assigned to: Michael Hudson (mwh)
Summary: 'is' does not work on methods

Initial Comment:
As of Python 2.4.2 (gcc 3.3.6, linux 2.6.13), the 'is'
comparison operator does not work on instancemethods or
classmethods (though it does work on staticmethods).
For example:

"""
>>> class A(object):
...   def foo(self): pass
...
>>> id(A.foo) == id(A.foo)
True
>>> A.foo is A.foo
False
>>>
>>> a = A()
>>> id(a.foo) == id(a.foo)
True
>>> a.foo is a.foo
False
"""

This example is applicable to old-style classes and
new-style classes, though things get more complicated
in the case of built-in types:

"""
>>> d = dict()
>>> id(d.update) == id(d.update)
True
>>> d.update is d.update
False
>>>
>>> id(dict.update) == id(dict.update)
True
>>> dict.update is dict.update
True
"""

However, using the classmethod 'fromkeys':

"""
>>> d = dict()
>>> id(d.fromkeys) == id(d.fromkeys)
True
>>> d.fromkeys is d.fromkeys
False
>>>
>>> id(dict.fromkeys) == id(dict.fromkeys)
True
>>> dict.fromkeys is dict.fromkeys
False
"""

----------------------------------------------------------------------

>Comment By: Michael Hudson (mwh)
Date: 2006-01-09 11:39

Message:
Logged In: YES 
user_id=6656

'is' is working just fine here.  When you execute 'a.foo' a fresh bound method 
object is made, so two executions lead to two different objects.  The thing 
that probably confused you was this:

>>> id(a.foo) == id(a.foo)
True

What happens here is that you execute 'a.foo' which returns a bound method 
object, you call id() on it, the bound method gets deleted, you execute 'a.foo' 
again and call id() on the new bound method object -- which happens to be 
allocated at the same place in memory as the previous one, so the id()s are 
the same.

Closing.

----------------------------------------------------------------------

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