On Aug 4, 6:48*am, Tobiah <t...@tobiah.org> wrote:
> I have a bunch of classes from another library (the html helpers
> from web2py). *There are certain methods that I'd like to add to
> every one of them. *So I'd like to put those methods in a class,
> and pass the parent at the time of instantiation. *Web2py has
> a FORM class for instance. *I'd like to go:
>
> * * * * my_element = html_factory(FORM)
>
> Then my_element would be an instance of my class, and also
> a child of FORM.

I've lately begun to prefer composition over inheritance for
situations like this:

class MyElementFormAdapter(object):
def __init__(self, form):
self.form = form

def render_form(self):
self.form.render()

my_element = MyElementFormAdapter(FORM)
my_element.render_form()
my_element.form.method_on_form()

Advantages include being more simple and obvious than multiple
inheritance, and avoiding namespace clashes:

class A(object):
def foo(self):
print 'a'

class B(object):
def foo(self):
print 'b'

class InheritFromAB(A, B):
pass

class AdaptAB(object):
def __init__(self, a, b):
self.a = a
self.b = b

>>> inherit = InheritFromAB()
>>> inherit.foo()
a
>>> adapt = AdaptAB(A(), B())
>>> adapt.a.foo()
a
>>> adapt.b.foo()
b