Question

I have the following code:

class A(object):
    def __init__(self):
        self.name = "A"
        super(A, self).__init__()

    def Update(self):
        print "Update A"
        self.PickTarget()

    def PickTarget(self):
        print "PickTarget A"

class B(object):
    def __init__(self):
        self.name = "B"
        super(B, self).__init__()

    def Update(self):
        print "Update B"
        self.PickTarget()

    def PickTarget(self):
        print "PickTarget B"

class C(A, B):
    def __init__(self):
        super(C, self).__init__()

    def Update(self, useA):
        if useA:
            A.Update(self)
        else:
            B.Update(self)

c = C()

c.Update(useA = True)
# prints: 
# Update A
# PickTarget A

c.Update(useA = False)
# prints:
# Update B
# PickTarget A

Why does calling C.Update with useA=False still call into A.PickTarget? How can I make this work how I want it to work (ie B.Update always calls into B.PickTarget)? I’m sure this has been asked before but my searching turned up nothing – probably because I don’t know what to search for.

Answer 1

It’s because A is before B in C‘s base classes.

You need to use B.PickTarget(self) rather than self.PickTarget() in B.Update(self) to get this behavior. Otherwise, switch A and B in C‘s definition.

Edit:

If the intended behavior is for B to always call methods in B and for A to always call methods in A, it’s correct to use A.method(self) instead of self.method(), as the second form doesn’t imply that method is in A.

You should redesign your classes. A should have a move method that moves the robot randomly and define it’s other basic behavior. B should be a subclass of A and should have a move method that calls super(B, self).move() if it doesn’t have a path, and otherwise moves on the path. This is the proper way to override a method on a condition.