Python: nested classes

A nested class can be created and used outside the class that it contains by fully qualifying its name:

#!/usr/bin/python3

class TQ84():

    class Nested():
        def __init__(self, name):
            self.name = name

        def __str__(self):
           return 'TQ84.Nested, name = ' + self.name

n = TQ84.Nested('foo')
print(n)
#
# TQ84.Nested, name = foo

Interestingly, even if the nested class is used within the class that contains it, its name still needs to be fully qualifed (in the following example, that is either self.Nested or CLS.Nested):

#!/usr/bin/python3

class CLS():

    class Nested():
        def __init__(self, name):
            self.name = name

        def __str__(self):
            return 'CLS.Nested, name = ' + self.name

    def __init__(self, name, name_nested):
        self.name = name
     #
     #  Note: Even though B.Nested is nested within
     #  class B, Nested needs to be qualified with
     #  either self.Nested or B.Nested!
     #
        self.nested = CLS.Nested(name_nested)

    def __str__(self):
        return 'CLS, name = ' + self.name + ' - ' + str(self.nested)

inst = CLS('bar', 'baz')
print(inst)
#
# CLS, name = bar - CLS.Nested, name = baz