Python : How to "merge" two class

Question

I want to add some attributes and methods into various class. The methods and attributes that I have to add are the same but not the class to assign them, so I want to construct a class who assign new methods and attributes for a class given in argument. I try this but it's not working: (I know that is a very wrong way to try to assign something to self, it's just to show what I want to do)

class A:
    def __init__(self):
        self.a = 'a'

    def getattA(self):
        return self.a

class B:
    def __init__(self, parent) :
        self = parent

        # This is working :
        print self.getattA()

    def getattB(self):
        return self.getattA()

insta = A()
instb = B(insta)

# This is not working :
print instb.getattB()

The result is :

a
Traceback (most recent call last):
  File "D:\Documents and settings\Bureau\merge.py", line 22, in <module>
    print instb.getattB()
  File "D:\Documents and settings\Bureau\merge.py", line 16, in getattB
    return self.getattA()
AttributeError: B instance has no attribute 'getattA'

And I expected to got 'a' for the call of instb.gettattB()

To resume I want to inherit class B from class A giving class A in argument of class B because my class B will be a subclass of various class, not always A.

Answer 1

I was having trouble with calling different constructors, using super doesn't necessarily make sense in a case like this, I opted to inherit and call each constructor on the current object manually:

class Foo(object):
    def __init__(self, foonum):
        super(Foo, self).__init__()
        self.foonum = foonum


class Bar(object):
    def __init__(self, barnum):
        super(Bar, self).__init__()
        self.barnum = barnum

class DiamondProblem(Foo, Bar):
    # Arg order don't matter, since we call the `__init__`'s ourself.
    def __init__(self, barnum, mynum, foonum):
        Foo.__init__(self, foonum)
        Bar.__init__(self, barnum)

        self.mynum = mynum