Question

Suppose one decided (yes, this is horrible) to create handle input in the following manner: A user types in a command on the python console after importing your class, the command is actually a class name, the class name’s __str__ function is actually a function with side effects (e.g. the command is “north” and the function changes some global variables and then returns text describing your current location). Obviously this is a stupid thing to do, but how would you do it (if possible)?

Note that the basic question is how to define the __str__ method for a class without creating an instance of the class, otherwise it would be simple (but still just as crazy:

class ff:
    def __str__(self):
        #do fun side effects
        return "fun text string"

ginst = ff()

>>ginst

Answer 1

What you are looking for is the metaclass

class Magic(type):
    def __str__(self):
        return 'Something crazy'
    def __repr__(self):
        return 'Another craziness'

class Foo(object):
    __metaclass__ = Magic

>>> print Foo
Something crazy
>>> Foo
Another craziness