Python笔记5-字典

1、建立字典

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

2、使用字典 （1）访问字典

方括号表示法

new_points=alien_0['points']
print(f"You just earned {new_points} points!")#You just earned 5 points!

get()：若指定的键可能不存在，应考虑使用get()

speed_value=alien_0.get('speed','No speed value assigned.')
print(speed_value)                            #No speed value assigned.

（2）添加与删除键值对

添加

alien_0['x_position']=0
alien_0['y_position']=25
print(alien_0)#{'color': 'green', 'points': 5, 'x_position': 0, 'y_position': 25}

删除

del alien_0['points']
print(alien_0)#{'color': 'yellow', 'x_position': 0, 'y_position': 25}
alien_0.clear()#清除
print(alien_0)#{}

（3）修改字典中的值

alien_0['color']='yellow'#修改
print(f"The alien is now {alien_0['color']}")#The alien is now yellow

（4）由类似对象组成的字典

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

3、遍历字典

user_0={
    'username':'efermi',
    'first':'enrico',
    'last':'fermi',
}

（1）遍历键值对

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

（2）遍历所有键

for key in user_0.keys():#遍历所有键
    print(f"Key:{key}") 
#Key:username
#Key:first
#Key:last

（3）按序遍历所有键

for key in sorted(user_0.keys()):#按序遍历所有键
    print(f"Key:{key}")
#Key:first
#Key:last
#Key:username

（4）遍历所有值

for value in user_0.values():#遍历所有值
    print(f"Value:{value}")
#Value:efermi
#Value:enrico
#Value:fermi

4、嵌套 （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)

（2）在字典中存储列表

pizza={
  'crust':'thick',
  'toppings':['musroooms','extra cheese'],
}
print(f"You ordered a {pizza['crust']}-crust pizza with the following toppings:")
for topping in pizza['toppings']:
  print("\t"+topping)
#You ordered a thick-crust pizza with the following toppings:
        #musroooms
        #extra cheese

（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,users_info in users.items():
    print(f"\nUsername:{username}")
    full_name=f"{users_info['first']} {'last'}"
    location=users_info['location']
    print(f"\tFull name:{full_name.title()}")
    print(f"\tLocation:{location.title()}")
#Username:aeinstein
#        Full name:Albert Last
#        Location:Princeton

#Username:mcurie
#        Full name:Marie Last
#        Location:Paris

(4)用用户输入来填充字典

responses={}
polling_active=True   #设置一个标志指出调查是否继续
while polling_active:  #提示输入被调查者的名字和回答
  name=input("\nWhat is your name?")
  response=input("Which mountain would you like to climb someday?")
  responses[name]=response#将回答存在字典中
  repeat=input("Would you like to let another person respond?(Yes/No)")#看是否还有人参与调查
  if repeat=='No':
​    polling_active=False
#调查结束显示结果
print("\n---Poll Result---")
for name,response in responses.items():
  print(f"{name} would like to climb {response}")
#What is your name?L
#Which mountain would you like to climb someday?Mountain Tai
#Would you like to let another person respond?(Yes/No)Yes

#What is your name?J
#Which mountain would you like to climb someday?Mountain Hua
#Would you like to let another person respond?(Yes/No)No

#---Poll Result---
#L would like to climb Mountain Tai
#J would like to climb Mountain Hua