cls & self

Diez B. Roggisch deets at nospam.web.de
Fri Jul 27 12:50:43 CEST 2007


james_027 schrieb:
> hi,
> 
> is cls & self the same thing?
> 
> I have seen something like
> 
> class A:
>     def dosomething(cls):
>        #doing something
> 
> How is cls & self differ? How is it use?

cls and self are just names. And you most certainly haven't seen the 
above, but this instead:

class A(object):
     @classmethod
     def dosomething(cls):
         pass


The decorator "classmethod" makes a method of a class a class-method. 
That means that it's not invoked like this

a = A()
a.dosomething()

but

A.dosomething()

instead. Common usage are e.g. factory methods. And because it is a 
classmethod, it gets the class passed as first argument, not the instance.


Diez



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