python - refactoring - generalizing derived classes

Question

I have following piece of code in Python. There are two classes A2 and B2 which share functions f1() and f2(). They differ in their base classes, deriving from A and B respectively.

I can see how to generalize this in C++ using templates. But I am not sure how to do this Python.

class A2(A):   
    def __init__(self):   
        A.__init__(self)   
        self._Z = Z('high')

    def f1(self):   
        return self._Z.f1() 

    def f2(self):   
        return self._Z.f2() 

    # ... more functions ...


class B2(B):   
    def __init__(self):   
        B.__init__(self)   
        self._Z = Z('low')

    def f1(self):   
        return self._Z.f1() 

    def f2(self):   
        return self._Z.f2() 

    # ... more functions ...

jme · Accepted Answer · 2015-12-02 19:55:39Z

3

If I understand your question, you might try a mixin class:

class Mixin(object):

    def f1(self):   
        return self._Z.f1() 

    def f2(self):   
        return self._Z.f2() 


class A2(A, Mixin): 

    def __init__(self):   
        A.__init__(self)   
        self._Z = Z('high')


class B2(B, Mixin):   
    def __init__(self):   
        B.__init__(self)   
        self._Z = Z('low')

answered Dec 2, 2015 at 19:55

jme

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6 Comments

Anand Over a year ago

Is there a way to avoid Multiple Inheritance?

Lukas Graf Over a year ago

@Anand have A and B inherit from Mixin. But why?

chepner Over a year ago

Python does not have the same problems with multiple inheritance that C++ does.

Anand Over a year ago

@LukasGraf Little scared of Multiple inheritance. Can this be solved using metaprogramming methods?

jme Over a year ago

@Anand Yes, it can. For instance, you could use a class decorator to define the common methods. But mixin classes are an establish pattern in Python, and are the simplest solution to your dilemma. Metaprogramming is cool, but simplicity > cool.

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