Passing a function as an argument from within the same class?

[Steven D'Aprano]

On Fri, 01 May 2009 07:35:40 -0700, zealalot wrote:

> So, I'm trying to come up with a way to pass a method (from the same
> class) as the default argument for another method in the same class.
> Unfortunately though, I keep getting "self not defined" errors since the
> class hasn't been read completely before it references itself.
> 
> Is there a better way of doing this?

My first instinct is to say "Don't do that!", but let's see if there's a 
way to get what you want. It's actually very easy: just put the 
definition of the passed method before the method you want to use it in, 
then refer to it by name *without* self.

However, there is a catch: you need to manually pass in the instance, 
instead of letting Python do it for you.

class Spam(object):
    def ham(self):
        return "ham"
    def spam(self, func=ham):
        return "spam is a tasty %s-like food product" % func(self)


And in use:

>>> obj = Spam()
>>> obj.ham()
'ham'
>>> obj.spam()
'spam is a tasty ham-like food product'



-- 
Steven