10. 解决方案：For 循环

练习解决方案：创建用户名 

names = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]
usernames = []

for name in names:
    usernames.append(name.lower().replace(" ", "_"))

print(usernames)

输出： 

['joey_tribbiani', 'monica_geller', 'chandler_bing', 'phoebe_buffay']

练习解决方案：使用 Range 修改用户名 

usernames = ["Joey Tribbiani", "Monica Geller", "Chandler Bing", "Phoebe Buffay"]

for i in range(len(usernames)):
    usernames[i] = usernames[i].lower().replace(" ", "_")

print(usernames)

输出： 

['joey_tribbiani', 'monica_geller', 'chandler_bing', 'phoebe_buffay']

练习解决方案：标记计数器

你可以使用字符串索引判断每个令牌是否以尖括号开始和结束。 

tokens = ['<greeting>', 'Hello World!', '</greeting>']

count = 0
for token in tokens:
    if token[0] == '<' and token[-1] == '>':
        count += 1

print(count)

输出： 

2

练习解决方案：创建 HTML 列表 

items = ['first string', 'second string']

html_str = "<ul>\n"
for item in items:
    html_str += "<li>{}</li>\n".format(item)
html_str += "</ul>"

print(html_str)

输出： 

<ul>
<li>first string</li>
<li>second string</li>
</ul>

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