CODEWITHSUNDEEP
pythonpython-2.7inheritancesuper
flakes
flakes

Reputation: 23644

Forcing base class functions to be used from the base class

The answer to this question is probably "W-what!? What the !@#$-- Stop!! That's a terrible idea!", but I would like to hear your thoughts...

I have two classes and one inherits from the other.

class A(object):
    def t1(self):
        self.t2()
    def t2(self):
        print "A"

class B(A):
    def t1(self):
        super(B, self).t1()
    def t2(self):
        print "B"

>>> a = A()
>>> b = B()
>>> a.tl()
A
>>> b.t1()
B

In this example B.t1 calls the super function, to call A.t1, but when it hits self.t2(), in the A.t1 function it returns to the B class to perform B.t2()

How would I be able to force calls from the base class to stay in the base class? This is all I could come up with, and it works, but I'm thinking there's a better solution.

class A(object):
    def t1(self):
        if type(self) == A:
            self.t2()
        else:
            super(type(self), self).t2()
    def t2(self):
        print "A"

class B(A):
    def t1(self):
        super(B, self).t1()
    def t2(self):
        print "B"

>>> a = A()
>>> b = B()
>>> a.tl()
A
>>> b.t1()
A

Upvotes: 0

Views: 44

Answers (2)

Ghislain Hivon
Ghislain Hivon

Reputation: 131

You use double underscore aka name mangling. 

class A(object):
    def t1(self):
        self.__t2()  # <---- changed the call
    def t2(self):
        print "A"

    __t2 = t2  # private copy of original t2() method

>>> a = A()
>>> b = B()
>>> a.tl()
A
>>> b.t1()
A

But name mangling has a huge default : it make unittesting more difficult and ugly if the function has only the double underscore as name.

But I'm with @BrenBarn, it feel like a fragile design.

Upvotes: 1

BrenBarn
BrenBarn

Reputation: 251448

In A's t1 you can do A.t2(self). However, this kind of setup is probably an indicator of a fragile design.

Upvotes: 1

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