Is it a bad practice to change the number of arguments of an overridden class method in Python?

Let's say I have a class written in Python like this:

class Foo(object):
    """My fake class"""

    def mymethod(self, first_arg):
        """original method"""
        pass

Now let's say I define a new class that extends the previous one and I want to override mymethod:

class Bar(Foo):
    """My new class"""

    def mymethod(self, first_arg, second_arg):
        """overridden method"""
        return first_arg == second_arg

Is it a bad practice to change the number of arguments in the overridden method?

EDIT:

Is there any official "good practice" rule about this? I just saw that if you do something like this in pydev you get a warning, so I suppose there should be something "official".