20201225-1

1-1
# Making a dictionary 
alien_0 = {'color': 'green', 'points': 5} 

2-1
# Getting the value associated with a key 
alien_0 = {'color': 'green', 'points': 5} 
 
print(alien_0['color']) 
print(alien_0['points'])

2-2
# Getting the value with get() 
alien_0 = {'color': 'green'} 
 
alien_color = alien_0.get('color') 
alien_points = alien_0.get('points', 0)                 
 
print(alien_color) 
print(alien_points) 

注：知识点链接
https://www.cnblogs.com/azxsdcv/p/14187824.html

3-1
# Adding a key-value pair 
alien_0 = {'color': 'green', 'points': 5} 
 
alien_0['x'] = 0 
alien_0['y'] = 25 
alien_0['speed'] = 1.5 

3-2
# Adding to an empty dictionary 
alien_0 = {} 
alien_0['color'] = 'green' 
alien_0['points'] = 5 

4-1
# Modifying values in a dictionary 
alien_0 = {'color': 'green', 'points': 5} 
print(alien_0) 
 
# Change the alien's color and point value. 
alien_0['color'] = 'yellow' 
alien_0['points'] = 10 
print(alien_0) 

5-1
# Deleting a key-value pair 
alien_0 = {'color': 'green', 'points': 5} 
print(alien_0) 
 
del alien_0['points'] 
print(alien_0) 

注：知识点链接
https://www.cnblogs.com/azxsdcv/p/14187824.html

6-1
# Looping through all key-value pairs 
# Store people's favorite languages. 
fav_languages = {     
    'jen': 'python',     
    'sarah': 'c',     
    'edward': 'ruby',     
    'phil': 'python',     
    } 
 
# Show each person's favorite language. 
for name, language in fav_languages.items():     
    print(name + ": " + language) 

注：知识点链接
https://www.cnblogs.com/azxsdcv/p/14187824.html

6-2    
# Looping through all the keys 
# Show everyone who's taken the survey. 
for name in fav_languages.keys():     
    print(name) 

注：知识点链接
https://www.cnblogs.com/azxsdcv/p/14187824.html

6-3
# Looping through all the values 
# Show all the languages that have been chosen. 
for language in fav_languages.values():     
    print(language) 

注：知识点链接
https://www.cnblogs.com/azxsdcv/p/14187824.html

6-4
# Looping through all the keys in order 
# Show each person's favorite language,  
#   in order by the person's name. 
for name in sorted(fav_languages.keys()):     
    print(name + ": " + language) 

7-1
# Finding a dictionary's length 
num_responses = len(fav_languages)

8-1
# Storing dictionaries in a list 
# Start with an empty list. 
users = [] 
 
# Make a new user, and add them to the list. 
new_user = {     
    'last': 'fermi',     
    'first': 'enrico',     
    'username': 'efermi',     
    } 
users.append(new_user) 
 
# Make another new user, and add them as well. 
new_user = {     
    'last': 'curie',     
    'first': 'marie',     
    'username': 'mcurie',     
    } 
users.append(new_user) 
 
# Show all information about each user. 
for user_dict in users:     
    for k, v in user_dict.items():         
        print(k + ": " + v)     
    print("
")  

8-2
# You can also define a list of dictionaries directly, without using append(): 
# Define a list of users, where each user 
#   is represented by a dictionary. 
users = [     
    {         
        'last': 'fermi',         
        'first': 'enrico',         
        'username': 'efermi',     
        },     
        {         
            'last': 'curie',         
            'first': 'marie',         
            'username': 'mcurie',     
            }, 
            ] 
 
# Show all information about each user. 
for user_dict in users:     
    for k, v in user_dict.items():         
        print(k + ": " + v)     
    print("
") 
注：为什么要先写入列表？因为一个字典的键值不能重复，列表可以包含多个字典；这种方式就可以重复了

9-1
# Storing lists in a dictionary 
# Store multiple languages for each person. 
fav_languages = {     
    'jen': ['python', 'ruby'],     
    'sarah': ['c'],     
    'edward': ['ruby', 'go'],     
    'phil': ['python', 'haskell'], 
    } 
 
# Show all responses for each person. 
for name, langs in fav_languages.items():     
    print(name + ": ")     
    for lang in langs:         
        print("- " + lang) 

10-1
Storing dictionaries in a dictionary 
users = {     
    'aeinstein': {         
        'first': 'albert',         
        'last': 'einstein',         
        'location': 'princeton',         
        },     
    'mcurie': {         
        'first': 'marie',         
        'last': 'curie',         
        'location': 'paris',         
        },     
    } 
 
for username, user_dict in users.items():     
    print("
Username: " + username)     
    full_name = user_dict['first'] + " "     
    full_name += user_dict['last']     
    location = user_dict['location'] 
 
    print("	Full name: " + full_name.title())     
    print("	Location: " + location.title()) 

11-1
Using an OrderedDict
# Standard Python dictionaries don't keep track of the order in which keys and values are added; 
# they only preserve the association between each key and its value. 
# If you want to preserve the order in which keys and values are added, use an OrderedDict. 
# Preserving the order of keys and values 
from collections import OrderedDict 
 
# Store each person's languages, keeping 
#  track of who respoded first. 
fav_languages = OrderedDict() 
 
fav_languages['jen'] = ['python', 'ruby'] 
fav_languages['sarah'] = ['c'] 
fav_languages['edward'] = ['ruby', 'go'] 
fav_languages['phil'] = ['python', 'haskell'] 
 
# Display the results, in the same order they were entered. 
for name, langs in fav_languages.items():     
    print(name + ":")     
    for lang in langs:         
        print("- " + lang) 

12-1
Generating a million dictionaries

# You can use a loop to generate a large number of dictionaries efficiently, 
# if all the dictionaries start out with similar data. 
# A million aliens 
aliens = [] 
 
# Make a million green aliens, worth 5 points 
#  each. Have them all start in one row. 
for alien_num in range(1000000):     
    new_alien = {}     
    new_alien['color'] = 'green'     
    new_alien['points'] = 5     
    new_alien['x'] = 20 * alien_num     
    new_alien['y'] = 0     
    aliens.append(new_alien) 
 
# Prove the list contains a million aliens. 
num_aliens = len(aliens) 
 
print("Number of aliens created:") 
print(num_aliens)