Where's the documentation to support the following behavior...

Benjamin Kaplan benjamin.kaplan at case.edu
Tue Mar 17 23:36:16 CET 2009


On Tue, Mar 17, 2009 at 6:14 PM, grocery_stocker <cdalten at gmail.com> wrote:

> Given the following....
>
> [example of cached numbers]
>
>
> It seems like id(list[<some value>]) == id(<some value>). However, I
> can't find anything in the python documentation that talks about it.
> Did I perhaps overlook something?


You didn't find anything because there's nothing to find. The fact that "7
is 7" is an implementation detail- CPython caches small numbers (I believe
<256) and some strings to boost performance. This isn't necessarily true of
Python in general.

Python 2.6.1 (r261:67515, Dec  9 2008, 14:03:29)
[GCC 4.0.1 (Apple Inc. build 5484)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 7
>>> b = 7
>>> id(a)
8405312
>>> id(b)
8405312
>>> a is b
True


IronPython 1.1 (1.1) on .NET 2.0.50727.1433
Copyright (c) Microsoft Corporation. All rights reserved.
>>> a = 7
>>> b = 7
>>> id(a)
43L
>>> id(b)
44L
>>>a is b
False


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