get timestamp string, length can only between 0 and 16

def get_timestamp(str_len=13):
    """ get timestamp string, length can only between 0 and 16
    """
    if isinstance(str_len, integer_types) and 0 < str_len < 17:
        return builtin_str(time.time()).replace(".", "")[:str_len]

    raise ParamsError("timestamp length can only between 0 and 16.")