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《Python编程：从入门到实践》读书笔记：第6章字典_【美】 eric matthes 著《 python 编程——从入门到实践》第六章。

作者：知新_RL | 2024-08-20 14:38:28

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【美】 eric matthes 著《 python 编程——从入门到实践》第六章。

第6章字典

6.1 一个简单的字典


alien_0 = {'color': 'green', 'points': 5}
 
print(alien_0['color'])
print(alien_0['points'])


green
5

6.2 使用字典

在Python中，字典是一系列键值对。每个键都与一个值相关联，你可使用键来访问相关联的值。

6.2.1 访问字典中的值


alien_0 = {'color': 'green', 'points': 5}
 
new_points = alien_0['points']
print(f'You just earned {new_points} points!')

You just earned 5 points!

6.2.2 添加键值对

字典是一种动态结构，可随时在其中添加键值对。要添加键值对，可一次指定字典名、用方括号括起的键和相关联的值。


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, 'x_position': 0, 'y_position': 25}

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


alien_0 = {}
 
alien_0['color'] = 'green'
alien_0['points'] = 5
 
print(alien_0)
print(f"The alien is {alien_0['color']}.")
 
alien_0['color'] = 'yellow'
print(f"The alien is now {alien_0['color']}.")


{'color': 'green', 'points': 5}
The alien is green.
The alien is now yellow.


alien_0 = {'x_position': 0, 'y_position': 25, 'speed': 'medium'}
print(f"Original position: {alien_0['x_position']}")
 
# 向右移动外星人。
# 根据当前速度确定将外星人向右移动多远。
 
if alien_0['speed'] == 'slow':
    x_increment = 1
elif alien_0['speed'] == 'medium':
    x_increment = 2
else:
    x_increment = 3
 
# 新位置为旧位置加上移动距离
alien_0['x_position'] = alien_0['x_position'] + x_increment
print(f"New position: {alien_0['x_position']}")


Original position: 0
New position: 2

6.2.5 删除键值对


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


{'color': 'green', 'points': 5}
{'color': 'green'}

删除的键值对会永远消失。

6.2.6 由类似对象组成的字典


favorite_language = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}
 
language = favorite_language['sarah'].title()
print(f"Sarah's favorite language is {language}.")

Sarah's favorite language is C.

6.2.7 使用get()来访问值


alien_0 = {'color': 'green', 'speed': 'slow'}
print(alien_0['points'])


    print(alien_0['points'])
KeyError: 'points'


alien_0 = {'color': 'green', 'speed': 'slow'}
 
point_value = alien_0.get('points', 'No point value assigned.')
print(point_value)

No point value assigned.

6.3 遍历字典

字典可用于以各种方式存储信息，因此有多种遍历方式：可遍历字典的所有键值对，也可仅遍历键或值。

6.3.1 遍历所有键值对


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


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


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


Jen's favorite language is Python
Sarah's favorite language is C
Edward's favorite language is Ruby
Phil's favorite language is Python

6.3.2 遍历字典中的所有键


favorite_language = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}
 
for name in favorite_language.keys():
    print(name.title())
 
print('\n')
for name in favorite_language:
    print(name.title())


Jen
Sarah
Edward
Phil
 
 
Jen
Sarah
Edward
Phil


 
for name in favorite_languages.keys():
    print(f"Hi {name.title()}.")
 
    if name in friends:
        language = favorite_languages[name].title()
        print(f"\t{name.title()}, I see you love {language}!")


Hi Jen.
Hi Sarah.
	Sarah, I see you love C!
Hi Edward.
Hi Phil.
	Phil, I see you love Python!


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

Erin, please take our poll!

6.3.3 按特定顺序遍历字典中的所有键


favorite_languages = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}
 
 
for name in sorted(favorite_languages.keys()):
    print(f"{name.title()}, thank you for taking the poll!")

6.3.4 遍历字典中的所有值


favorite_languages = {
    'jen': 'python',
    'sarah': 'c',
    'edward': 'ruby',
    'phil': 'python',
}
 
print('The following languages have been mentioned:')
for language in favorite_languages.values():
    print(language.title())


The following languages have been mentioned:
Python
C
Ruby
Python


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


The following languages have been mentioned:
Python
Ruby
C

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}


aliens = []
 
# 创建爱30个绿色的外星人
for alien_number in range(30):
    new_alien = {'color': 'green', 'points': 5, 'speed': 'slow'}
    aliens.append(new_alien)
 
# 显示前5个外星人
for alien in aliens[:5]:
    print(alien)
 
print('...')
print(f"Total number of aliens: {len(aliens)}")


{'color': 'green', 'points': 5, 'speed': 'slow'}
{'color': 'green', 'points': 5, 'speed': 'slow'}
{'color': 'green', 'points': 5, 'speed': 'slow'}
{'color': 'green', 'points': 5, 'speed': 'slow'}
{'color': 'green', 'points': 5, 'speed': 'slow'}
...
Total number of aliens: 30


# 创建一个用于存储外星人的空列表
aliens = []
 
# 创建爱30个绿色的外星人
for alien_number in range(30):
    new_alien = {'color': 'green', 'points': 5, 'speed': 'slow'}
    aliens.append(new_alien)
 
for alien in aliens[:3]:
    if alien['color'] == 'green':
        alien['color'] = 'yellow'
        alien['speed'] = 'medium'
        alien['points'] = 10
 
# 显示前5个外星人
for alien in aliens[:5]:
    print(alien)
print('...')


{'color': 'yellow', 'points': 10, 'speed': 'medium'}
{'color': 'yellow', 'points': 10, 'speed': 'medium'}
{'color': 'yellow', 'points': 10, 'speed': 'medium'}
{'color': 'green', 'points': 5, 'speed': 'slow'}
{'color': 'green', 'points': 5, 'speed': 'slow'}
...

6.4.2 在字典中存储列表


# 存储所点比萨的信息
pizza = {
    'crust': 'thick',
    'toppings': ['mushrooms', 'extra cheese'],
}
 
# 概述所点的比萨
print(f"You ordered a {pizza['crust']}-crust pizza with the following toppings:")
for topping in pizza['toppings']:
    print(topping)


You ordered a thick-crust pizza with the following toppings:
mushrooms
extra cheese


favorite_language = {
    'jen': ['python', 'ruby'],
    'sarah': ['c'],
    'edward': ['ruby', 'go'],
    'phil': ['python', 'haskell'],
}
 
for name, languages in favorite_language.items():
    print(f"\n{name.title()}'s favorite languages are:")
    for language in languages:
        print(f"\t{language.title()}")


Jen's favorite languages are:
	Python
	Ruby
Sarah's favorite languages are:
	C
 
Edward's favorite languages are:
	Ruby
	Go
Phil's favorite languages are:
	Python
	Haskell

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'
    }
}
 
for username, user_info in users.items():
    print(f"\nUsername: {username}")
 
    full_name = f"{user_info['first']} {user_info['last']}"
    location = user_info['location']
 
    print(f"\tFull name: {full_name.title()}")
    print(f"\tLocation: {location.title()}")


Username: aeinstein
	Full name: Albert Einstein
	Location: Princeton
 
Username: mcurie
	Full name: Marie Curie
	Location: Paris

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《Python编程：从入门到实践》读书笔记：第6章 字典_【美】 eric matthes 著《 python 编程——从入门到实践》第六章。

第6章 字典

6.1 一个简单的字典

6.2 使用字典

6.2.1 访问字典中的值

6.2.2 添加键值对

6.2.3 先创建一个空字典

6.2.4 修改字典中的值

6.2.5 删除键值对

6.2.6 由类似对象组成的字典

6.2.7 使用get()来访问值

6.3 遍历字典

6.3.1 遍历所有键值对

6.3.2 遍历字典中的所有键

6.3.3 按特定顺序遍历字典中的所有键

6.3.4 遍历字典中的所有值

6.4 嵌套

6.4.1 字典列表

6.4.2 在字典中存储列表

6.4.3 在字典中存储字典

《Python编程：从入门到实践》读书笔记：第6章字典_【美】 eric matthes 著《 python 编程——从入门到实践》第六章。

第6章字典