Is behavior of += intentional for int?

Terry Reedy tjreedy at
Wed Sep 2 02:00:16 CEST 2009

Steven D'Aprano wrote:
> I'm asking what *problem* you are trying to solve with mutable numbers, 
> where immutable numbers are not satisfactory. The only answer I can 
> imagine is that you're worried about the overhead of creating new integer 
> objects instead of just flipping a few bits in an existing integer 
> variable.

Of course, *because ints are immutable*, an implementation can avoid the 
overhead of object creation for common cases by creating an array of 
small integers.

CPython currently does this for -10 (or -5?) to about 256 or 257. I 
would not be surprised if this coevers at least 80% of int.__new__ requests.


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