1、字典中键-值为一对,keys()返回一个列表,包含字典中所有键,values()返回所有值
favorite_languages ={
'jack':"python",
'alex':"c",
'james':"ruby"
}
for key in favorite_languages.keys():
print(key)
print(list(favorite_languages.keys()))
for value in favorite_languages.values():
print(value)
print(list(favorite_languages.values()))
2、给字典添加键-值对
favorite_languages ={
'jack':"python",
'alex':"c",
'james':"ruby"
}
favorite_languages['paul']='c++'
favorite_languages['charlie']='c'
print('favorite_language is :'+str(favorite_languages['charlie']))
print(favorite_languages['paul'])
print("Paul's favorite_language is %s."%favorite_languages['paul'])
3、items()返回一个键—值对列表;
favorite_languages ={
'jack':"python",
'alex':"c",
'james':"ruby"
}
for k,v in favorite_languages.items():
print('\nK:'+k)
print('V:'+v)
4、keys()--键列表的应用
#遍历键列表
for key in favorite_languages.keys():
print('\n'+key.title())
#检查一个朋友是否在键列表中
friends=['jack','james']
for name in favorite_languages.keys():
print('\n'+name.title())
if name in friends:
print('Hi '+name.title()+',I see your favorite language is '+
favorite_languages[name].title() + '!')
else:
print(name.title(),',please take our poll.')
#按顺序遍历字典中所有键
for name in sorted(favorite_languages.keys()):
print(name.title())
5、set()集合的方式输出列表,集合中每个元素必须独一无二
#values()值列表应用
favorite_languages ={
'jack':"python",
'alex':"c",
'james':"c"
}
languages=[]
for language in set(favorite_languages.values()):
print(language.title())
languages.append(language)
print(languages)
6、嵌套:列表中嵌套字典
#将两个字典循环插入空列表30次
resumes=[]
for resume_number in range(30):
new_resume1={'name':'jack','age':'','living_city':'beijing'}
new_resume2={'name':'alex','age':'','living_city':'shanghai'}
resumes.append(new_resume1)
resumes.append(new_resume2)
for resume in resumes[:3]:
print(resume)#依次输出前三个字典
if resume['name'] == 'jack':#按条件修改字典中的值
resume['name']='james'
resume['age']=''
resume['living_city']='zhengzhou'
elif resume['name'] == 'alex':
resume['name']='paul'
resume['age']=''
resume['living_city']='shenzhen'
print(resume)#依次输出修改后的前三个字典
print('The number of new resumes is %s.'%str(len(resumes)))#输出列表长度
7、字典中嵌套列表
#字典的值为列表
favorite_flowers={
'jack':['rose','lily','peony'],
'alex':'lily',
'james':['lily','peony','tulip']
}
for name,flowers in favorite_flowers.items():#遍历字典
print('\n',len(flowers))#输出值的长度
if len(flowers) > 1:#如果长度大于1,就为列表
print(name.title()+"'s favorite flower are:")
for flower in flowers:
print('\t',flower.title())
else: #否则就是单个字符串
print(name.title()+"'s favorite flower is:")
print('\t',flowers[0].title())
8、字典中嵌套字典
#字典的值为字典
people={
'eric':{'name':'eric','age':'','location':'beijing'},
'james':{'name':'james','age':'','location':'shanghai'}
}
for person,info in people.items():#遍历字典
print('\nUsername:',person) #依次输出键
for k,v in info.items(): #遍历嵌套字典的键值对
print('%s:%s'%(k,v))
print('------------')
9、setdefault()--括号内的值可以是key活着key,value,如果字典中有key,输出对应的值,如果括号内的key不存在,就给字典添加一个key,value值默认为None;
这个函数尽量不要用,容易出错
user_info = {
'jack':'c',
'alex':'c++'
}
print(user_info.setdefault('jack'))
print(user_info.setdefault('james','python'))
print(user_info)
10、fromkeys()只是借用一个字典的格式来生成一个新的字典,不改变借用字典,这个函数尽量不要用
popitem() 随机删除字典中的键-值对;尽量不要用
user_info = {
'jack':'c',
'alex':'c++'
}
print(user_info.fromkeys([1,2,3,4],'aaaa'))
print(user_info)
print(user_info.popitem())#随机删除字典中的键-值对;尽量不要用
print(user_info)
11、update()根据新的字典更新老的字典,已存在的键值对,根据第二个字典改变,没有的就添加进来,一切以第二个为准
user_info = {
'jack':'c',
'alex':'c++'
}
user_info2 = {
'alex':'python',
'paul':'java'
}
user_info.update(user_info2)#update()根据新的字典更新老的字典
print(user_info)
12、dic.get(key)函数获取字典的value,如果key不存在,就返回None,不会报错,如果直接用dic[key]=value,如果字典为空,就会报错。
dic = {}
print(dic.get("key"))
#None