Python 编程 从入门到实践》 第六章 字典

第 六 章 字典

区别： 列表 ：方括号，元组：圆括号，字典：花括号

字典 是一系列键、值对，每个键 都与一个值相关联。
可以使用键来访问与之相关联的值，与键相关联的值可以是数字、字符串、列表乃至字典。

6.2.1　访问字典中的值

alien_0 = {‘color’: ‘green’} #'color’为键， 'green’为值
print(alien_0[‘color’])

6.2.2　添加键—值对

先指定字典，然后将键用方括号括起来，并对于相关联的值

alien_0 = {‘color’: ‘green’, ‘points’: 5}
print(alien_0)
alien_0[‘x_position’] = 0
alien_0[‘y_position’] = 25
print(alien_0)

{‘color’: ‘green’, ‘points’: 5}
{‘color’: ‘green’, ‘points’: 5, ‘y_position’: 25, ‘x_position’: 0} #顺序与添加顺序不同

6.2.3　先创建一个空字典

alien_0 = {}

alien_0[‘color’] = ‘green’
alien_0[‘points’] = 5
print(alien_0)

{‘color’: ‘green’, ‘points’: 5}

6.2.4　修改字典中的值

和添加类似

alien_0 = {‘color’: ‘green’}
print("The alien is " + alien_0[‘color’] + “.”)
alien_0[‘color’] = ‘yellow’
print("The alien is now " + alien_0[‘color’] + “.”)

The alien is green.
The alien is now yellow.

6.2.5　删除键—值对

使用del 语句将相应的键—值对彻底删除

alien_0 = {‘color’: ‘green’, ‘points’: 5}
print(alien_0)
del alien_0[‘points’]
print(alien_0)

{‘color’: ‘green’, ‘points’: 5}
{‘color’: ‘green’}

6.2.6　由类似对象组成的字典

favorite_languages = { # 人名和他喜欢的语言
‘jen’: ‘python’,
‘sarah’: ‘c’,
‘edward’: ‘ruby’,
‘phil’: ‘python’,
}

print("Sarah’s favorite language is " +
favorite_languages[‘sarah’].title() +
“.”)

Sarah s favorite language is C.

6.3　遍历字典

user_0 = {
‘username’: ‘efermi’,
‘first’: ‘enrico’,
‘last’: ‘fermi’,
}

for key, value in user_0.items(): #key, value可以换成任意两个字符变量
　print("\nKey: " + key)
　print("Value: " + value)

Key: last
Value: fermi
Key: first
Value: enrico
Key: username
Value: efermi

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() + “.”)

Phils favorite language is Python.
Phils favorite language is Python.
Phils favorite language is Python.
Phils favorite language is Python.

6.3.2　遍历字典中的所有键

for name in favorite_languages.keys(): #keys()可以省略
　print(name.title())

6.3.3　按顺序遍历字典中的所有键

使用函数sorted() 来获得按特定顺序排列的键列表的副本

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

6.3.4　遍历字典中的所有值

for language in favorite_languages.values(): # 可使用set(favorite_languages.values() 剔除重复的值
　print(language.title())

6.4　嵌套

6.4.1　字典列表

alien_0 = {‘color’: ‘green’, ‘points’: 5}
alien_1 = {‘color’: ‘yellow’, ‘points’: 10}
alien_2 = {‘color’: ‘red’, ‘points’: 15}
aliens = [alien_0, alien_1, alien_2]
for alien in aliens:
　print(alien)

{‘color’: ‘green’, ‘points’: 5}
{‘color’: ‘yellow’, ‘points’: 10}
{‘color’: ‘red’, ‘points’: 15}

6.4.2　在字典中存储列表

pizza = {
‘crust’: ‘thick’,
‘toppings’: [‘mushrooms’, ‘extra cheese’],
}

6.4.3　在字典中存储字典

users = {
‘aeinstein’: {
‘first’: ‘albert’,
‘last’: ‘einstein’,
‘location’: ‘princeton’,
},
‘mcurie’: {
‘first’: ‘marie’,
‘last’: ‘curie’,
‘location’: ‘paris’,
},
}