Paul Rubin wrote:
> I'm trying the super() function as described in Python Cookbook, 1st
> ed, p. 172 (Recipe 5.4).
>
> class A(object):
> def f(self):
> print 'A'
>
>
> class B(object):
> def f(self):
> print 'b'
>
>
> class C(A,B):
> def f(self):
Typo? 'c' should be 'C' in:
> super(c,self).f()
> print 'C'
>
> def test(cls):
> x = cls()
> x.f()
>
> test(C)
>
> I have the impression that this is supposed to call the f method
> in both A and B, so it should print
> A
> B
> C
> or maybe
> B
> A
> C
> depending on the resolution order. However, it only calls A.f and not
> B.f.
You misunderstand. A single call to super only calls the next method in the
chain. You have to include calls to super at all levels except for the
ultimate base class.
>
> I also notice that if I say
>
>
> class B(object):
> def f(self):
> super(B,self).f()
> print 'b'
>
> then
> test(B)
> raises an exception since B has no superclass with an f method. That
> doesn't seem like such a good thing necessarily.
You have to terminate the chain somehow. e.g.
class MyBase(object):
def f(self):
print "MyBase"
class A(MyBase):
def f(self):
super(A, self).f()
print "A"
...
class B(MyBase):
def f(self):
super(B, self).f()
print "B"
...
>
> Anyway, is there a preferred way of writing this example so that C.f
> automatically calls both A.f and B.f?
The trick is that C.f only calls A.f, but A.f needs to end up calling B.f
when it is used in a C.
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