Python multiple inheritance questions

Question

Sorry if this question has been asked before, I could not find the answer while searching other questions.

I'm new to Python and I'm having issues with multiple inheritance. Suppose I have 2 classes, B and C, which inherit from the same class A, which are defined as follows:

class B(A):
 def foo():
 ...
 return
 def bar():
 ...
 return
class C(A):
 def foo():
 ...
 return
 def bar():
 ...
 return

I now want to define another class D, which inherits from both B and C. D should inherit B's implementation of foo, but C's implementation of bar. How do I go about doing this?

• Mike McMahon: this is known as the diamond problem - mypythonnotes.wordpress.com/2008/11/01/…
• m.wasowski: it is better to explicitly say what do you want, in D.__init__ you can self.bar = C.bar
• Padraic Cunningham: super().foo() in class D will call B.foo() once B is before C in the mro
• jez: @m.wasowski I think it would be better to do this directly in the class definition than to do it on an instance-by-instance basis at __init__ time.

Answer 1

Resisting the temptation to say "avoid this situation in the first place", one (not necessarily elegant) solution could be to wrap the methods explicitly:

class A: pass
class B( A ):
 def foo( self ): print( 'B.foo')
 def bar( self ): print( 'B.bar')
class C( A ):
 def foo( self ): print( 'C.foo')
 def bar( self ): print( 'C.bar')
class D( B, C ):
 def foo( self ): return B.foo( self )
 def bar( self ): return C.bar( self )

Alternatively you can make the method definitions explicit, without wrapping:

class D( B, C ):
 foo = B.foo
 bar = C.bar