[Tutor] Re: Re: Factory classes (etc)

[Magnus Lycka]

At 08:09 2002-09-04 -0700, Emile van Sebille wrote:
> > Python doesn't let you do method overloading?
>
>Python isn't going to do it for you, but you can.
>
>def test(a,b):
>     try: return a*1., b+""
>     except:
>         try: return a+"", b*1.
>         except:
>             raise 'invalid args'

In general it's a bad idea to use exceptions for other
things than error handling. They cost a lot of performance.

This might be a better solution (assuming that you don't
use keyword arguments):

def typesAreSame(recievedArgs, expectedArgs):
     if len(recievedArgs) !=3D len(expectedArgs):
         return 0
     for recievedArg, expectedArg in zip(recievedArgs, expectedArgs):
         if type(recievedArg) !=3D type(expectedArg):
             return 0
     return 1

(You might want to extent that a bit to check that instances are
of correct class.)

class X:
     def needsOverloading(self, *args):
         if typesAreSame(args, (1,1,1)):
             self.___threeIntegersMethod(self, *args)
         elif typesAreSame(args, ("")):
             self.___oneStringMethod(self, *args)
         ...
         else:
             raise ValueError, 'Bad parameters: %s' % args

But in most cases where you use overloading or templates in
C++ etc, you just write one method in Python, and that's it! :)
Perhaps you need an extra if-statement in the method, but I
have never missed method overloading in Python during the six
years I used it.


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