id( ) function question

Laszlo Nagy gandalf at
Wed Oct 14 22:37:27 CEST 2009

> Andre Engels schrieb:
>> What is going on is that a few objects that are often used, in
>> particular the small (how small is small depends on the
>> implementation) integers, are 'preloaded'. When one of these is then
>> referred to, a new object is not created, but the pre-defined object
>> is used. 10 is apparently a preloaded constant in your implementation,
>> 1e10 is not.
>> As far as I know, only None is _guaranteed_ to be such a preloaded
>> object, so one should not rely on it in implementations.
> None, True, False, NotImplemented are guaranteed to be singletons, all
> builtin types and exceptions can be considered as singletons, too.
I thought that different mutable objects always have different ids. If 
this is not true, then what the id() function is used for? What useful 
thing can we do with it?



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