def is_number(arg):
    '''
    is_number(x) yields True if x is a numeric object and False otherwise.
    '''
    return (is_number(mag(arg)) if is_quantity(arg)              else
            is_npscalar(arg, 'number') or is_npvalue(arg, 'number'))
is_number(x) yields True if x is a numeric object and False otherwise.