[Edu-sig] Consistency question
Guido van Rossum
guido at python.org
Wed Sep 24 20:18:04 EDT 2003
> My understanding is that int(5.0) actually triggers __int__ -- a method
> inherited by all floats.
> When I go dir(5.0), I see __int__ listed, and I can go:
> >>> 5.0 .__int__()
> So far so good.
> But then I can also go int('123') and get back 123. So why isn't __int__ a
> method of string objects?
> >>> '123' .__int__()
> gets me an error, and dir('') doesn't show __int__ as being among string's
> I'd like to clear up this confusion because I'm writing some tutorial
> materials. What I don't understand, I can't rightly explain.
int() special-cases various argument types. It only calls __int__
when none of the special cases apply. An argument of type str is a
special case (as is an argument of type unicode) because in that case,
and *only* that case, the optional second 'base' argument is accepted.
(If you really want to know more, RTSL. :-)
--Guido van Rossum (home page: http://www.python.org/~guido/)
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