[已解决]求助！练习：创建用户名

class_bool

原问题：写一个遍历 names 列表以创建 usernames 列表的 for 循环。要为每个姓名创建用户名，使姓名全小写并用下划线代替空格。对以下列表运行 for 循环：
names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
应该会创建列表：
usernames = ["joey_tribbiani", "monica_geller", "chandler_bing", "phoebe_buffay"]


我的代码
names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
usernames = []
i = 0
for i in range(len(names)):
    usernames[i] = names[i].lower()
    x = usernames[i].find(' ')
    usernames[i] = usernames[i][:x] + '_' + usernames[i][x:]
print(usernames)


报错
IndexError: list assignment index out of range

最佳答案

月排行榜 / 总排行榜

Twilight6

2022-2-6 11:24:26

usernames 列表初始化时为 空列表，导致一开始 usernames[i ] 赋值超出索引值，导致报错

可以在初始化时候将列表创建好指定长度，即可：

1. names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
   
2. usernames = [0] * len(names)
   
3. for i in range(len(names)):
   
4.     usernames[i] = names[i].lower()
   
5.     x = usernames[i].find(' ')
   
6.     usernames[i] = usernames[i][:x] + '_' + usernames[i][x+1:]
   
7. print(usernames)

复制代码

或者直接使用 append 函数，同2楼代码：

1. names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
   
2. usernames = []
   
3. for i in range(len(names)):
   
4.     usernames.append(names[i].lower())
   
5.     x = usernames[i].find(' ')
   
6.     usernames[i] = usernames[i][:x] + '_' + usernames[i][x+1:]
   
7. print(usernames)

复制代码

跳转到最佳答案楼层

isdkz

列表为空的时候不能用索引的方式赋值

1. names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
   
2. usernames = []
   
3. i = 0
   
4. for i in range(len(names)):
   
5.     usernames.append(names[i].lower())     # 修改这一行代码
   
6.     x = usernames[i].find(' ')
   
7.     usernames[i] = usernames[i][:x] + '_' + usernames[i][x:]
   
8. print(usernames)
   

复制代码

傻眼貓咪

1. names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
   
2. usernames = [name.lower().replace(' ', '_') for name in names]
   
3. print(usernames)

复制代码

Twilight6

usernames 列表初始化时为 空列表，导致一开始 usernames[i ] 赋值超出索引值，导致报错

可以在初始化时候将列表创建好指定长度，即可：

1. names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
   
2. usernames = [0] * len(names)
   
3. for i in range(len(names)):
   
4.     usernames[i] = names[i].lower()
   
5.     x = usernames[i].find(' ')
   
6.     usernames[i] = usernames[i][:x] + '_' + usernames[i][x+1:]
   
7. print(usernames)

复制代码

或者直接使用 append 函数，同2楼代码：

1. names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
   
2. usernames = []
   
3. for i in range(len(names)):
   
4.     usernames.append(names[i].lower())
   
5.     x = usernames[i].find(' ')
   
6.     usernames[i] = usernames[i][:x] + '_' + usernames[i][x+1:]
   
7. print(usernames)

复制代码