[Python-Dev] Re: Re: Caching objects in memory

[Terry Reedy]

Guido:

But for *immutable* objects (like numbers, strings and tuples) the
implementation is free to use caching. In practice, I believe ints
between -5 and 100 are cached, and 1-character strings are often
cached (but not always).

Hope this helps! I would think this is in the docs somewhere but
probably not in a place where one would ever think to look...

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I am sure that the fact that immutables *may* be cached is in the ref 
manual, but I have been under the impression that the private, *mutable* 
specifics for CPython are intentionally omitted so that people will not 
think of them as either fixed or as part of the language/library.

I have previously suggested that there be a separate doc for CPython 
implementation details like this that some people want but which are not 
part of the language or library definition.

Terry J. Reedy