六、Python字典

Python学习笔记

参考书目：《Python编程从入门到实践（第2版）》，[美] Eric Matthes，袁国忠译

六、字典

在Python中，字典是一系列的键值对。与键相关联的值可以是数、字符串、列表乃至字典。
字典用{ }，列表是[ ]。集合也是{ }，但集合中没有键值对，不同于字典和列表，集合中的元素没有顺序。

1、使用字典

1）访问字典中的值

alien_0 = {'color':'green','points':5}  # 键值对之间用逗号分隔
new_points = alien_0['points']
print(f"You just earn {new_points} points!")

You just earn 5 points!

2）添加键值对

alien_0['x_position'] = 0
alien_0['y_position'] = 25
print(alien_0)

{‘color’: ‘green’, ‘points’: 5, ‘x_position’: 0, ‘y_position’: 25}

3）删除键值对

del alien_0['y_position']
print(alien_0)

{‘color’: ‘green’, ‘points’: 5, ‘x_position’: 0}

4）使用get访问值，可以在指定的值不存在时返回默认值

print_value = alien_0.get('speed','No speed value assigned.')
print_value_0 = alien_0.get('speed')
print(print_value)
print(print_value_0)

No speed value assigned.
None

2、遍历

1）遍历所有键值对

user_0 = {
    'jen':'python',
    'sarah':'c',
    'phil':'python',
}
for k, v in user_0.items():  # items()返回键值对列表
    print(f"\nName:{k}")
    print(f"Favoriate:{v}")

Name:jen
Favoriate:python

Name:sarah
Favoriate:c

Name:phil
Favoriate:python

2）遍历所有键

for key in user_0.keys():
    print(key)
# 遍历字典会默认遍历所有键
for key_1 in user_0:
    print(key_1)

jen
sarah
phil
jen
sarah
phil

# 按特定顺序遍历所有键
for k in sorted(user_0.keys()):
    print(k)

jen
phil
sarah

3）遍历所有值

for value in user_0.values():
    print(value)

python
c
python

4）遍历并剔除重复项

for v in set(user_0.values()):
    print(v)

python
c

3、嵌套

1）字典列表

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

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

2）在字典中添加列表

user_0 = {
    'jen':['python','c++'],
    'sarah':['c'],
    'phil':['python','ruby'],
}
for name, languages in user_0.items():
    print(f"{name}'s favorate language are:")
    for language in languages:
        print(f"\t{language}")

jen’s favorate language are:
python
c++
sarah’s favorate language are:
c
phil’s favorate language are:
python
ruby