Explaining names vs variables in Python

[Steven D'Aprano]

On Thu, 3 Mar 2016 12:48 am, Chris Angelico wrote:

> On Thu, Mar 3, 2016 at 12:39 AM, Marko Rauhamaa <marko at pacujo.net> wrote:
>> Chris Angelico <rosuav at gmail.com>:
>>
>>> Python defines that every object has an identity, which can be
>>> represented as an integer. Since this is an intrinsic part of the
>>> object, no two distinct objects can truly have identical
>>> characteristics. Python's objects are like rifles - there are many
>>> like it, but this one is mine.
>>
>> How can you be sure Python isn't returning the same id value for two
>> distinct objects?

The language is entitled to re-use IDs provided the objects do not exist at
the same time. So there certainly will be times that Python will return the
same ID for different objects:

py> id([1])
3083419340L
py> id([2])
3083419340L



> The same way I can be sure about anything else in Python. It's a
> language guarantee. If you're bothered by that, you should also be
> concerned that str(x) might not actually call x.__str__(), 

Technically, it doesn't, it calls type(x).__str__() (at least in Python 3
and new-style classes in 2) :-)


But your point is broadly correct: you trust the language to do what it
promises, or you look for evidence that it doesn't and report a bug if you
find it.



-- 
Steven