Question

My base code looks like this:

class C1(object):
    def f(self):
    return 2*self.g()

    def g(self):
    return 2

class C2(C1):
    def f(self):
    return 3*self.g()


class C3(C1):
    def g(self):
        return 5

class C4(C3):
    def f(self):
    return 7*self.g()

obj1 = C1()
obj2 = C2()
obj3 = C3()
obj4 = C4()

Now my question is the following: I need to write three assignment statements that do the following:

• assign the calling list for obj2.f() to the variable obj2_calls
• assign the calling list for obj3.f() to the variable obj3_calls
• assign the calling list for obj4.f() to the variable obj4_calls

Calling list being for example, when obj1.f() is called, the f method of C1 is called which calls the g method of C1. This could be represented as a calling list of the form ['C1.f', 'C1.g']

I don’t quite know the proper way to write the assignment statements and I desperately want to help out my friend with her stuff.

If you could just show me how to properly right out the first assignment statement, I’m sure I could figure out the rest.

Answer 1

The key insight is that if a method is not defined for a class, it will default to use the method of a class that the class inherits.

Thus, ask yourself what ‘obj2.f()’ will do.

• What class is obj2? It is C2.
• Is there an f method defined for class C2? Yes, there is. So the method C2.f is called.
• The C2.f method calls self.g, which means it looks for C2.g. Is there a ‘C2.g’ method? No, so we have to go to the class that C2 inherits from. The line class C2(C1) tells us that it is inherited from the class C1, so it will call the method C1.g.

Those are the steps to get the first calling list; the rest are up to you.