Reusing object methods?

[Joal Heagney]

Axel Straschil wrote:
> Hello!
> 
> Why not:
> 
> 
>>class A:
>>     def a_lengthy_method(self, params):
>>          # do some work depending only on data in self and params
>>
>>class B(A): pass
> 
> 
> ?
> 
> Lg,
> AXEL.

As a rough guess, I think the original poster was wondering how to 
include *one* specific method from class A into B, without including all 
the methods of A. Jp Calderone's suggestion of defining a special Mixin 
class seems to be the cleanest implementation.

E.g.

class MyMixin:
	""" Defines only a single method. It may be a debug call, or
	a replacement for the classes' string representation. Etc. """
	def a_lengthy_method(self,params):
		# do some work

class A(MyMixin):
	def other_lengthy_procedures(self, params):
		pass

class B(MyMixin):
	pass

The advantage of this is that you can define a normal inheritance tree 
for a variety of classes, and then specifically override a single (or 
group) of methods by placing the MyMixin class at the front of the 
inheritance call. (The book "Programming Python" uses this a LOT in the 
Tkinter section.)

E.g.

class C:
	def well_now_what_do_we_do(self):
		# stuff
	def a_lengthy_method(self,params):
		# This does the wrong stuff.

class D(MyMixin, C):
	def __init__(self):
		# blahblahblah

Now class D has the "correct" a_lengthy_method, inherited from MyMixin, 
as well as all the other methods from class C, and the methods defined 
in it's own class statement.

Joal