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Class hierarchy problem in Python

0 votes

I have a hierarchy of classes (SubA, SubAB, SubB, ..., SubBCA, SubC,...), each of which is inheriting from a chain of superclasses with a common baseclass(Sup) on top. (So far, no problem)

Now, I want to create instances of the correct subclasstype as decided by the common baseclass, like this:

i = Sup(args_allowing_the_baseclass_to_deduce_correct_subclass)

where i can be of any class except Sup itself (as decided by Sup)

Now, the problem:

How to design the __new__() and __init__() methods for the various classes in order to achieve what I want?

posted Aug 6, 2013 by Deepankar Dubey

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Try  factory function instead of the class itself? Then all you need to do is call the appropriate class.

1 Answer

+1 vote

Keep it simple, use a function:

def make(*args):
 class_ = deduce_correct_class(*args)
 return class_(*args)

That way you won't even need any __new__() methods.

answer Aug 6, 2013 by Sumit Pokharna
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I would like to apply the method to a member of a class. Here is a small example that shows what I would like to do:

from multiprocessing import Pool

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l = range(10)

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using this with the normal map doesn't cause any problem

This fails because it says that the methods can't be pickled. (I assume it has something to do with the note in the documentation: "functionality within this package requires that the __main__ module be importable by the children.", which is obscure to me).

I would like to understand two things: why my code fails and when I can expect it to fail? what is a possible workaround?