ga.py

class Foo(object):

    def a(*args):
        return 'a', args

    def b(*args):
        return 'b', args

    def __init__(self):
        self.which = {'A' : self.a, 'B' : self.b}

    def _default(self, key):
        f = self.which[key]
        return f(key)

    def __getattr__(self, missing_attribute):
        return self._default


foo = Foo()

print foo.abc('A')

gistfile1.txt

$ python scratch/ga.py
('a', (<__main__.Foo object at 0x104098790>, 'A'))