rationale behind python class/subclass inheritance

Question

When I create a parent class and child class as shown below, why don't the arguments from the parent class automatically get pulled in by the child class?

I understand that explicit is better, but I'm wondering in what circumstance this code...

class testParent(object):
    def __init__(self,testParentParam1,testParentParam2):
        pass


class testChild(testParent):
    def __init__(self,testParentParam1,testParentParam2,testChildParam1,testChildParam2):
        pass

Is better than this code...

class testParent(object):
    def __init__(self,testParentParam1,testParentParam2):
        pass


class testChild(testParent):
    def __init__(self,testChildParam1,testChildParam2):
        pass

It's hard to tell which is better while the constructors are empty anyway. — bereal
– bereal, Commented Mar 25, 2013 at 15:04
Both can work, it depends on what you are trying to do. There is not enough info here to figure out where your problem is. — cmd
– cmd, Commented Mar 25, 2013 at 15:06
Few of the child classed I've written (that needed a __init__ of its own) accepted the same arguments as the superclass and passed them on unmodified. The majority accepted fewer arguments or different arguments (and somehow computed the arguments to pass to the superclass). — user395760
– user395760, Commented Mar 25, 2013 at 15:06

Fred Foo · Accepted Answer · 2013-03-25 15:07:33Z

4

Derived classes extend base classes. That means they might need more/less/different information at construction time to do their extending. Consider:

class BaseTextDocument(object):
    def __init__(self, content):
        self.content = content

class WordDocument(object):
    def __init__(self, path, word_version="guess_from_file"):
        content = parse_word_document(path, word_version)
        super(WordDocument, self).__init__(content)

answered Mar 25, 2013 at 15:07

Fred Foo

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