function overloading

[Alex Martelli]

Mirko Koenig wrote:

> Hi
> 
> I serached around the web and some tutorials but i can't finds any
> documentation about function overloading in python.

That may be because there is no such thing.


> I want to have 3 functions:
> def setPos( x, y ):
> 
> def setPos( pos ):
> 
> def setPos( object ):

You cannot have three different objects (for example, three different
functions) corresponding to the same name in the same scope.  One name,
one scope, one object.

> Is it not possible in python to overload fucntion with the same name?

Exactly!  Whenever you bind a name X to an object Y -- whether that
happens with a def statement, an assignment, or in other ways yet -- any
previous binding to the same name X in the same scope is simply forgotten.

> How do you do it?

We don't (bind several different objects to the same name in a given
scope).  If you're keen on being able to call setPos(x,y) as well as
setPos(pos) there are several ways you can achieve this effect -- e.g.

def setPos(x,y):
  "whatever"

setPos_2args = setPos

def setPos(pos):
   "whatever"

setPos_postype = setPos

def setPos(another):
   "whatever"

setPos_anyother = setPos

def setPos(*args):
    if len(args)==2: return setPos_2args(*args)
    if len(args)>1: raise TypeError
    if type(args[0]) == postype: return setPos_postype(*args)
    return setPos_anyother(*args)


Of course, it's quite unnatural and stilted to program in this way,
as is typical of such efforts to use the programming style appropriate
to language X while actually programming in very different language Y.
If you learn to program in Y's own style, you will be more productive
and generally happier.


Alex