nested classes - how to use function from parent class?

Question

If I have this situation:

class Foo(object):
    def __init__(self):
        self.bar = Bar()

    def do_something(self):
        print 'doing something'

    class Bar(object):
        def __init(self):
            self.a = 'a'

        def some_function(self):

I want to call do_something function inside some_function function but this function doesn't belong to the class, what can I do to call this function? I don't want to use it with Foo().do_something, there are another option? I don't want to create new instance

another example:

class A(object):
    def __init__(self):
        self.content = 'abcdabcabcabc'
        self.b = self.B()
        self.c = self.C()    

    def some_function(self):
        print self.content

    class B(object):
        def foo(self):
            A.some_function()

    class C(object):
        def foo(self):
            A.some_function()

http://stackoverflow.com/questions/1765677/nested-classes-scope — BugHunter, Mar 20 '17 at 10:42
`Foo` isn't `Bar`'s "parent". Nested classes in Python don't really gain you anything except an extra level of scoping. — martineau, Mar 20 '17 at 10:48
If you don't want to call it as an instance method then don't make it an instance method. — Stop harming Monica, Mar 20 '17 at 10:49
I edit my question with another example, what is the best way to do it? — Udi Goldberg, Mar 20 '17 at 11:50
You should not use nesteed classes to start with,a s I put here: http://stackoverflow.com/questions/42326408/python-how-to-get-a-list-of-inner-classes/42343825#42343825 — jsbueno, Mar 20 '17 at 12:22

score 0 · Accepted Answer · answered Mar 20 '17 at 12:33

There is no practical use case for nested classes in Python, but for scoping some class attributes with namespaces. And in that case, you should not create instances of them at all.

All you get if you have instances of nested classes is a headache - there is no benneffit. The "Outter" class won't see them as anything special - that is unlike in C++, from where it looks like this pattern originated, that the nested class is, in its whole, private to the container class.

The concept of being private in Python is done purely by convention, and if no other code than Foo should use instances of Bar, indicate that by calling it _Bar and in the documentation.

Other than that being nested won't help Bar to get a reference to Foo by any other means than through its name (ok, there are ways using the descriptor protocol, but it is not meant for this) - and them, if you want to run Foo.do_something without having a Foo instance, do_something should be a classmethod anyway.

Now, if you want to have aggregated objects, that is another thing. You have to do is:

class Bar(object):
    def __init(self, parent):
        self.parent = parent
        self.a = 'a'

    def some_function(self):
        self.parent.do_something(...)

class Foo(object):
    def __init__(self):
        self.bar = Bar(self)

    def do_something(self):
        print 'doing something'

nested classes - how to use function from parent class?

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