On 08/03/2012 10:25 AM, hyperboogie wrote:
Hello everyone.
This is my first post in this group.
I started learning python a week ago from the "dive into python" e-
book and thus far all was clear.
However today while reading chapter 5 about objects and object
orientation I ran into something that confused me.
it says here:
http://www.diveintopython.net/object_oriented_framework/defining_classes.html#fileinfo.class.example
"__init__ methods are optional, but when you define one, you must
remember to explicitly call the ancestor's __init__ method (if it
defines one). This is more generally true: whenever a descendant wants
to extend the behavior of the ancestor, the descendant method must
explicitly call the ancestor method at the proper time, with the
proper arguments. "
However later on in the chapter:
http://www.diveintopython.net/object_oriented_framework/userdict.html
it says:
"Methods are defined solely by their name, and there can be only one
method per class with a given name. So if a descendant class has an
__init__ method, it always overrides the ancestor __init__ method,
even if the descendant defines it with a different argument list. And
the same rule applies to any other method. "
My question is if __init__ in the descendant class overrides __init__
in the parent class how can I call the parent's __init__ from the
descendant class - I just overrode it didn't I?
Am I missing something more fundamental here?
Thanks
The mro function [Method Resolution Order]is not too well advertised in
the docs. This should illustrate its usage:
#!/usr/bin/env python
class A():
def __init__(self):
z= 1
def ringA(self):
print ('aaa')
def ringB(self):
print('bbb')
class B(A):
def __init__(self):
z= 2
def ringB(self):
print('BBB')
a= A()
b= B()
b.ringB()
b.ringA()
b.__class__.mro()[1].ringB(b)
z= 1
def main():
pass
if __name__ == '__main__':
main()
I'm not sure that the class initialization is required.
Good luck,
Colin W.
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