Scope and classes

David davidshais at googlemail.com
Wed Aug 19 01:38:15 CEST 2009


On Aug 19, 12:16 am, Chris Rebert <c... at rebertia.com> wrote:
> On Tue, Aug 18, 2009 at 3:47 PM, David<davidsh... at googlemail.com> wrote:
> > Hi all,
>
> > I'm trying to understand how scopes work within a class definition.
> > I'll quickly illustrate with an example. Say I had the following class
> > definition:
>
> > class Abc:
> >    message = 'Hello World'
>
> >    def print_message(self):
> >        print message
>
> >>>> instance = Abc()
> >>>> instance.print_message()
> > NameError: global name 'message' not defined
>
> > My question is, why? message is not defined in print_message, but it
> > is defined in the enclosing scope (the class)?
>
> A class' scope is never consulted when resolving variable names in its methods.
>
> The scopes consulted are roughly (and in this order):
> 1. Local variable scope (i.e. of the current function/method)
> 2. Enclosing functions (if you have functions nested inside other functions)
> 3. Globals (i.e. module-level variables)
> 3. Builtins (i.e. the built-in functions and methods, such as len())
>
> To access class-level variables from within instance methods of the
> class, you have 2 options:
> A. Use the class name, i.e. Abc.message
> B. Reference the class indirectly, i.e. self.__class__.message
>
> Cheers,
> Chris
> --http://blog.rebertia.com

Ah, thanks!



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