@classmethod
def preprocess(cls, modulus):
    modulus = sympify(modulus)
    if (modulus.is_Integer and (modulus > 0)):
        return int(modulus)
    else:
        raise OptionError(("'modulus' must a positive integer, got %s" % modulus))
@classmethod
def preprocess(cls, modulus):
    modulus = sympify(modulus)
    if (modulus.is_Integer and (modulus > 0)):
        return int(modulus)
    else:
        raise OptionError(("'modulus' must a positive integer, got %s" % modulus))