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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Reference
Date: Mon, 03 Mar 2014 13:48:39 -0500
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Xref: csiph.com comp.lang.python:67573

On 3/3/2014 4:42 AM, ast wrote:

> Consider following code:
>
>>>> A=7
>>>> B=7
>>>> A is B

The 'is' operator has three uses, two intended and one not. In 
production code, 'is' tests that an object *is* a particular singular 
object, such as None or a sentinel instance of class object. In test 
code, 'is' can also be used to test details of a particular 
implementation, such as pre-allocation of small ints. New python 
programmers also use it to confuse themselves.

-- 
Terry Jan Reedy