keeping a ref to a non-member function in a class

[Peter Otten]

Gregory Bond wrote:

> I'm building a class hierarchy that needs to keep as a class variable a
> reference to a (non-member) function, so that different subclasses can
> use different generator functions.  But it seems Python is treating the
> function as a member function because the reference to it is in class
> scope....
> 
> Here's a simple case of what I'm trying (in the real code, fn is a
> function that returns a database connection relevant to that subclass):
> 
>> def foo():
>>         print "foo called"
>> 
>> class S(object):
>>         fn = foo
>> 
>>         def bar(cls):
>>                 cls.fn()
>>         bar = classmethod(bar)
>> 
>> def foo2():
>>         print "foo2 called"
>> 
>> class D(S):
>>         fn = foo2
>> 
>> D.bar()

 
> I've tried playing with staticmethod() but I can't quite get it all
> worked out...

You are on the right track with staticmethod, but you have to apply it to
fn:

>>> def foo(): print "first foo"
...
>>> def foo2(): print "second foo"
...
>>> class S(object):
...     fn = staticmethod(foo)
...     def bar(cls):
...             cls.fn()
...     bar = classmethod(bar)
...
>>> class D(S):
...     fn = staticmethod(foo2)
...
>>> S.bar()
first foo
>>> D.bar()
second foo

In its current form, the bar() method is not necessary:

>>> S.fn()
first foo
>>> D.fn()
second foo

Peter