python循环问题报错（练习：创建用户名）

问题遇到的现象和发生背景

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"]

问题相关代码，请勿粘贴截图

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

运行结果及报错内容

Traceback (most recent call last):
File "vm_main3.py", line 47, in
import main
File "/tmp/vmuser_wkodhsoirj/main.py", line 2, in
import studentMain
File "/tmp/vmuser_wkodhsoirj/studentMain.py", line 1, in
import usernames
File "/tmp/vmuser_wkodhsoirj/usernames.py", line 4, in
usernames[i] = names[i].lower()
IndexError: list assignment index out of range

我的解答思路和尝试过的方法

我想要达到的结果

你的写法，逻辑有些乱

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

把变量命名改一下， 看起来会清晰一些

names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
username_list = []
for i in range(len(names)):
    username = names[i].lower()
    x = username.find(' ')
    username_list.append(username[:x] + '_' + username[x:])
print(username_list)

索引超范围了，空列表添加元素用append函数，别直接赋值

望被采纳

names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
usernames = []
for name in names:
    new_name = name.lower().replace(" ", "_")
    usernames.append(new_name)

print(usernames)