字符串按位数分割

# 以分割银行卡帐号为例，每四位以空格分割def SplitString(numberstring, num=4, sign=' '):    # 常常传入的数据转化为字符串    numstring = str(numberstring)    # 获取传入的截取长度个符号，开始的下标与结束下标    num = num    sign = sign    start_index = 0    end_index = num    str_list =[]    # 须要遍历的次数    len_str=int(len(numstring))    for i in range(int(len_str/num+1)):        str_list.append(numstring[start_index:end_index])        str_list.append(sign)        start_index = end_index        end_index += num    outstr = "".join(str_list)    len_outstr = len(outstr)    if len_str % num == 0:        last_outstr = outstr[0:len_outstr-2]    else:        last_outstr = outstr[0:len_outstr-1]    return last_outstr