def helper_ldexp(f, unit1, unit2):
    if (unit2 is not None):
        raise TypeError('Cannot use ldexp with a quantity as second argument.')
    else:
        return ([None, None], _d(unit1))
def helper_ldexp(f, unit1, unit2):
    if (unit2 is not None):
        raise TypeError('Cannot use ldexp with a quantity as second argument.')
    else:
        return ([None, None], _d(unit1))