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

The Best answer is in the comments, it was useful for me so I decided to show it in an answer (thank to sr2222):
The way to dynamicaly declare inherance in Python is the type() built-in function.
For my example :

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

    def getattA(self):
        return self.a, self.args

class B(object) :
    b = 'b' 
    def __init__(self, args) :
        self.b_init = args

    def getattB(self):
        return self.b

C = type('C', (A,B), dict(c='c'))

instc = C('args')

print 'attributes :', instc.a,  instc.args, instc.b, instc.c
print 'methodes :', instc.getattA(), instc.getattB()

print instc.b_init

The code return :

attributes : a args b c
methodes : ('a', 'args') b
Traceback (most recent call last):
  File "D:\Documents and settings\Bureau\merge2.py", line 24, in <module>
    print instc.b_init
AttributeError: 'C' object has no attribute 'b_init'

My class C inerhite attributes and methods of class A and class B and we add c attribute. With the instanciation of C (instc = C(‘args’)) The init for A is call but not for B.

Very useful for me because I have to add some attributes and methodes (the same) on different class.