'Returns the first derivative of a Heaviside Function.
Examples
>>> from sympy import Heaviside, diff
>>> from sympy.abc import x
>>> Heaviside(x).fdiff()
DiracDelta(x)
>>> Heaviside(x**2 - 1).fdiff()
DiracDelta(x**2 - 1)
>>> diff(Heaviside(x)).fdiff()
DiracDelta(x, 1)'

def fdiff(self, argindex=1):

    if (argindex == 1):
        return DiracDelta(self.args[0])
    else:
        raise ArgumentIndexError(self, argindex)
