2.3 遍历字典
遍历字典的方式: 1遍历字典的所有的键-值对
2遍历字典的键
3遍历字典的值
2.3.1 遍历所有的键-值对
user_0 = {'username':'efermi','first':'enrico','last':'fermi',}
获悉字典user_0中的所有信息 for循环
键和值可以为任何名称(变量):k,v
键和值的名称可以根据实际情况来命名,这样容易理解
items() 函数以列表返回可遍历的(键, 值) 元组。
将字典中的键值对以元组存储,并将众多元组存在列表中。
可以用list 函数将items 返回的可迭代序列转化为列表
list_1 = user_0.items() list(list_1)
结果:
Out[2]: [('username', 'efermi'), ('first', 'enrico'), ('last', 'fermi')]
返回值:[(‘username’, ‘efermi’), (‘first’, ‘enrico’), (‘last’, ‘fermi’)]
for key,value in user_0.items():print("\nKey: " + key)print("Value: " + value)
结果:
Key: usernameValue: efermiKey: firstValue: enricoKey: lastValue: fermi
或者
for k,v in user_0.items():print("\nKey: " + key)print("Value: " + value)
结果:
Key: lastValue: fermiKey: lastValue: fermiKey: lastValue: fermi
注意:键-值对的返回顺序可能与存储顺序不同,因为python不关心键-值对的存储顺序,
而只跟踪键和值之间的关联关系
favorite_languages = {'jen':'python','sarah':'c','edwaid':'ruby','phil':'python',}
键和值的名称可以根据实际情况来命名,这样容易理解
即键和值用描述性语句容易让人理解for循环中在作什么操作
for name,language in favorite_languages.items():print(name.title() + "'s favorite languages is " +language.title() + ".")
结果:
Jen's favorite languages is Python.Sarah's favorite languages is C.Edwaid's favorite languages is Ruby.Phil's favorite languages is Python.
2.3.2 变量字典中的键 方法keys()
keys函数是Python的字典函数,它返回字典中的所有键所组成的一个可迭代序列。
使用keys()可以获得字典中所有的键。
使用list()函数可将keys()函数返回的可迭代序列转化为列表
favorite_languages = {'jen':'python','sarah':'c','edwaid':'ruby','phil':'python',}for name in favorite_languages.keys():print(name.title())# 这四行代码等价for name in favorite_languages:print(name.title())
结果:
JenSarahEdwaidPhil
原因:遍历字典时,会默认遍历所有的键
方式keys()是显示的遍历键
将字典中的键存储到一个names列表中
names = []names_1 = list(favorite_languages.keys())for name in favorite_languages:t_names = namenames.append(t_names)print(name.title())print(names)print(names_1)
结果:
JenSarahEdwaidPhil['jen', 'sarah', 'edwaid', 'phil']['jen', 'sarah', 'edwaid', 'phil']
使用键遍历的例子:使用当前的键来访问与之相关联的值
favorite_languages = {'jen':'python','sarah':'c','edwaid':'ruby','phil':'python',}friends = ['phil','sarah']for name in favorite_languages.keys():print(name.title())if name in friends:print(" Hi " + name.title() +", I see your favorite language is " + favorite_languages[name].title() + "!")
结果:
JenSarahHi Sarah, I see your favorite language is C!EdwaidPhilHi Phil, I see your favorite language is Python!
使用keys()确定某个人是否接受了调查
favorite_languages = {'jen':'python','sarah':'c','edwaid':'ruby','phil':'python',}if 'erin' not in favorite_languages.keys():print("Erin,please take our poll!")
结果:
Erin,please take our poll!
2.3.3 按顺序遍历字典中的所有键sorted函数
favorite_languages = {'jen':'python','sarah':'c','edwaid':'ruby','phil':'python',}for name in sorted(favorite_languages.keys()):print(name.title() + ", thank you for taking the poll.")
结果:
Edwaid, thank you for taking the poll.Jen, thank you for taking the poll.Phil, thank you for taking the poll.Sarah, thank you for taking the poll.
2.3.4 遍历字典中的所有值方法values()
values()返回值:它返回字典中的所有值所组成的一个可迭代序列。
使用list可以去掉dict_value前缀,并转为列表
favorite_languages = {'jen':'python','sarah':'c','edwaid':'ruby','phil':'python',}print("The following languages have been mentioned: ")for language in favorite_languages.values():print(language.title())
结果:
The following languages have been mentioned: PythonCRubyPython
值去重,可考虑集和
print("The following languages have been mentioned: ")for language in set(favorite_languages.values()):print(language)list_languages = list(favorite_languages.values())print(type(list_languages))print(list_languages)
结果:
The following languages have been mentioned: pythonrubyc<class 'list'>['python', 'c', 'ruby', 'python']python,c,ruby,python
另一种遍历值的方法
value = favorite_languages.values()print(",".join(i for i in value))
结果:
python,c,ruby,python
2-4 嵌套
定义:将一系列字典存储在列表中,或将列表作为值存储在字典中,称为嵌套
2-4-1 字典列表 将字典存到列表中
4、存储字典的列表
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)
结果:
{'color': 'green', 'points': 5}{'color': 'yellow', 'points': 10}{'color': 'red', 'points': 15}
外星人有代码自动生成
创建一个用于存储外星人的空列表
aliens = []
创建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(".......")
结果:
{'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'}.......
显示创建了多个外星人
print("\nTotal number of aliens: " + str(len(aliens)))
结果:
Total number of aliens: 30
外星人都有相同特征,python中每个外星人都是独立的,所以我们可以对每个外星进行修改
修改前3个外星人特征
创建一个用于存储外星人的空列表
aliens = []
创建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(".......")
结果:
{'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'}.......
进一步扩展
创建一个用于存储外星人的空列表aliens = []
aliens = []
创建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'] = 10elif alien['color'] == 'yellow':alien['color'] = 'red'alien['speed'] = 'fast'alien['points'] = 15
显示前5个外星人
for alien in aliens[:10]:print(alien)print(".......")
结果:
{'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'}{'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'}.......
应用领域:在网站中位每一个用户创建一个字典,并将字典存储到列表中
(每个字典的结构相同)
遍历列表处理数据
2.4.2 在字典中存储列表 即字典中放列表
5、存储列表的字典
存储所点比萨的信息
pizza = {'crust':'thick','toppings':['mushrooms','extra cheese'],}
概述所点的比萨
print("You ordered a " + pizza['crust'] + "-crust pizza " +"With the following toppings: ")for topping in pizza['toppings']:print('\t' + topping)
结果:
You ordered a thick-crust pizza With the following toppings: mushroomsextra cheese
一个键关联多个值
favorite_languages = {'jen':['python','ruby'],'sarah':['c'],'edwaid':['ruby','go'],'phil':['python','haskell'],}for name,languages in favorite_languages.items():if len(languages) == 1:print("\n" + name.title() + "'s favorite language is " + languages[0].title()) # 注意只有一个元素在列表中时,要用下标0来获取最后一个元素else:print("\n" + name.title() + "'s favorite languages are: ")for language in languages:print("\t" + language.title())
结果:
Jen's favorite languages are: PythonRubySarah's favorite language is CEdwaid's favorite languages are: RubyGoPhil's favorite languages are: PythonHaskell
注意:列表和字典的嵌套层级不应该太多
太多的话,应该考虑有更简单的方法
6-4-3 在字典中存储字典
6、存储字典的字典
users = {'aeinstein':{'first':'albert','last':'einstein','location':'princeton',},'mcurie':{'first':"marie",'last':'curie','location':'paris',},}for username,user_info in users.items():print("\nUsername: " + username)full_name = user_info['first'] + " " + user_info['last']location = user_info['location']print("\tFull name: " + full_name.title())print("\tLocation: " + location.title())
结果:
Username: aeinsteinFull name: Albert EinsteinLocation: PrincetonUsername: mcurieFull name: Marie CurieLocation: Paris
总结:
1、字典的遍历方法:items()方法:键-值对遍历,返回的值是一个可以迭代序列,list()函数可以将其转为列表
keys()方法:键遍历,返回的值是一个可以迭代序列,list()函数可以将其转为列表
values()方法:值变量,返回值是一个可以迭代序列,list()函数可以将其转为列表
2、嵌套: 在列表中放字典,用于相同属性的对象
在字典中放列表,用于具有相同键的对象
在字典中放置地,用于复制对象
3、在Python对于可迭代的内置数据类型tuple,字符串若放在一个可迭代对象里面,最后一个字符串将以一个个字符变量,因为单个字符串也是可以迭代对象
例子:
tuple_2 = ('你好!')for ele in list_2:print(ele)
结果:
你好!