human
I wrote the below code

    class mytanh(Function, ):
        def fdiff(self, argindex=1):
            return (1 - (mytanh(self.args[0]) ** 2))
        @classmethod
        def eval(cls, arg):
            arg = sympify(arg)
            if (arg == 0):
                return sympify(0)
    e = tanh(x)
    f = mytanh(x)
    assert (tanh(x).series(x, 0, 6) == mytanh(x).series(x, 0, 6))

What's a good function header?
assistant
#Here's a good function header.

def test_function_series3():