selecting base class from user input

[Jackson]

I want a class that will determine its base class by the argument passed
in.  What I am about to write _does_not_work_, but it shows what I am
trying to do.

class ABC(some_super):
	def __init__(self,some_super):
            some_super.__init__(self)

            if some_super == list:
               self.append('ABC')

            elif some_super == dict:
               self['ABC'] = None


Then, the user can call this function:

>>> example = ABC(list)
>>> print example
['ABC']

>>> example = ABC(dict)
>>> print example
{'ABC': None}

Clearly, this is a bad example, but the central idea is what I am trying
to do.  ABC is a particular example which can be represented in various
forms.  I want an ABC class that will create the example in the form
specified by the user.

So how can I achieve this? Thanks.