> The following small program is giving me some unexpected results with
> Python 2.2.1:
>
> class Int(object):
> def __int__(self): return 10
>
> class Float(object):
> def __float__(self): return 10.0
>
> class Long(object):
> def __long__(self): return 10L
>
> class Complex(object):
> def __complex__(self): return (10+0j)
>
> def attempt(f,arg):
> try:
> return f(arg)
> except Exception,e:
> return str(e.__class__.__name__)+': '+str(e)
>
> for f in int,float,long,complex:
> for t in Int,Float,Long,Complex:
> print f.__name__ + '(' + t.__name__ + ')\t\t',
> print attempt(f,t())
>
> ----- results ------
>
> int(Int) 10
> int(Float) TypeError: object can't be converted to int
> int(Long) TypeError: object can't be converted to int
> int(Complex) TypeError: object can't be converted to int
>
> *** OK, int() seems to work as expected
>
> float(Int) TypeError: float() needs a string argument
> float(Float) 10.0
> float(Long) TypeError: float() needs a string argument
> float(Complex) TypeError: float() needs a string argument
>
> *** float() seems to work, but what's with the error message about strings?
Sloppy coding. float(), like int() and long(), takes either a number
or a string. Raymond Hettinger fixed this in CVS in response to SF
bug 551673, about two weeks ago. :-)
> long(Int) TypeError: object can't be converted to long
> long(Float) TypeError: object can't be converted to long
> long(Long) 10
> long(Complex) TypeError: object can't be converted to long
>
> **** OK, long seems to work as expected
>
> complex(Int) TypeError: complex() arg can't be converted to
> complex
> complex(Float) (10+0j)
> complex(Long) TypeError: complex() arg can't be converted to
> complex
> complex(Complex) TypeError: complex() arg can't be converted to
> complex
>
> **** I can understand complex() handling Float implicitly, but only if it
> also handles Complex! And if it does handle Float implicitly, shouldn't all
> of these handle everything?
The signature of complex() is different -- it takes two float
arguments, the real and imaginary part.
It doesn't take Complex() because of a bug: it only looks for
__complex__ if the argument is a classic instance. Maybe Raymond can
fix this? I've added a bug report: python.org/sf/563740
--Guido van Rossum (home page: http://www.python.org/~guido/)
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