operator "is"

[shigin]

BPO	1981
Nosy	@gvanrossum, @birkenfeld, @amauryfa

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2008-01-31.16:19:03.952>
created_at = <Date 2008-01-31.16:17:01.568>
labels = ['type-bug']
title = 'operator "is"'
updated_at = <Date 2008-02-01.16:04:22.063>
user = 'https://bugs.python.org/shigin'

bugs.python.org fields:

activity = <Date 2008-02-01.16:04:22.063>
actor = 'gvanrossum'
assignee = 'none'
closed = True
closed_date = <Date 2008-01-31.16:19:03.952>
closer = 'georg.brandl'
components = []
creation = <Date 2008-01-31.16:17:01.568>
creator = 'shigin'
dependencies = []
files = []
hgrepos = []
issue_num = 1981
keywords = []
message_count = 5.0
messages = ['61905', '61906', '61907', '61908', '61962']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'georg.brandl', 'amaury.forgeotdarc', 'shigin']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue1981'
versions = ['Python 2.5', 'Python 2.4']

[shigin]

Hello,

The operator "is" works strange with methods, i.e.:

>>> a = 1
>>> a.__abs__ is a.__abs__
False

If this is the preferred behavior by some reasons, I think
documentation should explain it.

It was tested on python 2.4.4, 2.5.1 and trunk r60477.

[birkenfeld]

Yes, it is expected since the descriptor access to methods creates a new
bound method object every time. The "is" operator does not work special
with methods.

There is another issue about documenting this, so closing as a duplicate.

[amauryfa]

It's actually documented in
http://docs.python.org/dev/reference/datamodel.html

"""
Note that the transformation from function object to (unbound or bound)
method object happens each time the attribute is retrieved from the
class or instance
"""

[shigin]

I think it's good idea to make a note in Comparisons section or make
some reference to data model section.

"""
The operators is and is not test for object identity: x is y is true if
and only if x and y are the same object. x is not y yields the inverse
truth value.
"""

But,
>>> id(a.__abs__) == id(a.__abs__)
True

And only example below shows me error in my objection.
>>> id(w)
6636344
>>> p = id(w)
>>> del w
>>> e = 1
>>> id(e)
6636344

I'm sorry for spam. I've missed bpo-1410739 when search for any open
bug.

[gvanrossum]

id(a.__abs__) == id(a.__abs__)

has a completely different explanation -- it so happens that the first
instantiation of a.__abs__ is freed after id() is called on it and the
second instantiation happens to reuse that same memory block.