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("\n")
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("\n")
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("\nUsername: " + username)
full_name = user_dict['first'] + " "
full_name += user_dict['last']
location = user_dict['location']
print("\tFull name: " + full_name.title())
print("\tLocation: " + 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)
