[Python-Dev] Semantics of __int__(), __index__()
hrvoje.niksic at avl.com
Wed Apr 3 14:47:31 CEST 2013
On 04/03/2013 01:17 PM, Nick Coghlan wrote:
> > > >
> > > I like Nick's answer to that: int *should* always return something of
> > > exact type int. Otherwise you're always left wondering whether you
> > > have to do "int(int(x))", or perhaps even "int(int(int(x)))", to be
> > > absolutely sure of getting an int.
> > Agreed.
> Perhaps we should start emitting a DeprecationWarning for int subclasses
> returned from __int__ and __index__ in 3.4?
Why would one want to be absolutely sure of getting an int?
It seems like a good feature that an __int__ implementation can choose
to return an int subclass with additional (and optional) information.
After all, int subclass instances should be usable everywhere where ints
are, including in C code. I can imagine numpy and similar projects
would be making use of this ability already -- just think of uses for
numpy's subclasses of "float".
If one wants to break the abstraction and be absolutely positively sure
of getting an int and not a subclass thereof, they can write something
like (0).__add__(obj). But I suspect this will be extremely rare.
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