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Class hierarchy problem in Python

0 votes
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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 want to build a class that perform various functions to the content(or lines) of any given file. I want to first include the opening and reading file function into that class, then add other methods.

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I would like to apply the Pool.map method to a member of a class. Here is a small example that shows what I would like to do:

from multiprocessing import Pool

class A(object):
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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?


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