遍历字典

1. 遍历所有键值对

eg1: 

user_0 = {
    'username': 'efermi',
    'first': 'enrico',
    'last': 'fermi',
}
for key, value in user_0.items():
    print("\nKey: " + key)
    print("Value: " + value)

for key, value in user_0.items(): 也可简化为 for k, v in user_0.items(): 但对于这两个变量是可以使用任何名称，并不局限于此。

eg2: 打印出每个人喜欢的语言

favorite_languages = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}
for name, language in favorite_languages.items():
    print(name.title() + "'s favorite language is " + language.title() + ".")

2.遍历字典中的所有键

for name in favorite_languages.keys():
    print(name.title())

或省略keys(),输出不变

for name in favorite_languages:
    print(name.title())

找出两位朋友喜欢的语言：

friends = ['phil', 'sarah']
for name in favorite_languages.keys():
    if name in friends:
        print("Hi " + name.title() + ", I see your favorite language is " + favorite_languages[name].title() + "!")

确定某个人是否接受了调查

if 'eric' not in favorite_languages.keys():
    print("Erin, please take our poll!")

3. 按顺序遍历字典中的所有键

for name in sorted(favorite_languages.keys()):
    print(name.title() + ", thank you for taking the poll.")

调用sorted( )函数让字典中所有键在遍历前排序。

4. 遍历字典中的所有值

print('The following languages have been mentioned:')
for language in favorite_languages.values():
    print(language.title())

运行结果：

The following languages have been mentioned:
Python
C
Ruby
Python

打印出了字典中的所有值，但字典中的值是可以重复的，结果也就出现了重复，为此可以使用集合set( )提出重复：

print('The following languages have been mentioned:')
for language in set(favorite_languages.values()):
    print(language.title())

运行结果：

The following languages have been mentioned:
Python
Ruby
C

Note: 遍历字典时，键值的返回顺序是不定的，键和值的对应是固定。