Is it possible to do partial inheritance with Python?

Question

I\'m creating a class (class0) in Python that is a currently based off of one class (class1); however, I\'d like to inherit from another class as well (class2). The thing ab

Answer 1

create another base class implementing this one method and make class2 and class1 both inherit this class

Answer 2

The "mixin" method of having another class that just implemetns the method you want is the correct thing to do in this case. But for sake of completeness, as it answers exactly what you are asking, I add that yes, it is possible to have a behavior just like the "partial inheritance" you want (but note that such a concept does not exist formally).

All one have to do is to add member on the new class that refer to to the method or attribute you wish to repeat there:

class Class2(object):
   def method(self):
      print ("I am method at %s" % self.__class__)

class Class1(object):
   pass

class Class0(Class1):
   method = Class2.__dict__["method"]

ob = Class0()
ob.method()

Note that retrieving the method from the class __dict__ is needed in Python 2.x (up to 2.7) - due to runtime transforms that are made to convert the function in a method. In Python 3.0 and above, just change the line

method = Class2.__dict__["method"]

to

method = Class2.method

Answer 3

Why don't you use composition instead? Have your class keep a reference to the desired object, and delegate to it.

Answer 4

One path is to use the 'mixin' approach:

class Mixin(object):
    def method(self):
        pass

class C1(Mixin, ...parents...):
    pass

class C2(Mixin, ...parents...):
    pass

Another way is the composition:

class C1(object):
    def method(self):
        pass

class C2(object):
    def __init__(self):
        self.c1 = C1()

    def method(self):
        return self.c1.method()