3-3 字典

1、字典的定义

stu_info = {"name":"王志华","age":18,"addr":"北京"}
# key - value

2、查询

#查
print(stu_info)
print(stu_info['name'])
print(stu_info['age'])
print(stu_info['money'])  #取key不存在的 KeyError: 'money'

3、修改元素

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
#修改
stu_info['addr'] ='上海'
print(stu_info)

4、新增字典元素

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
#新增
stu_info['phone'] = 1234567
stu_info.setdefault('email','sfsfs@163.com')
#你用setdefault新增一个已经存在的key,它不会改变原来key的value
stu_info.setdefault('age',29)
print(stu_info)
#{'name': '王志华', 'age': 18, 'addr': '北京', 'phone': 1234567, 'email': 'sfsfs@163.com'}

5、删除字典元素

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
#删除
stu_info.pop('addr')
del stu_info['age']  #
stu_info.clear() #清空这个字典
stu_info.popitem()#从字典里面随机删除一个元素
print(stu_info)

6、合并两个字典

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
#删除
stu_info.pop('addr')
del stu_info['age']  #
stu_info.clear() #清空这个字典
stu_info.popitem()#从字典里面随机删除一个元素
print(stu_info)
8 #{'b': 1, 'a': 'v'}

7、获取字典中所有的key值和value值

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
print(stu_info.keys())   #获取字典里面所有的key
# dict_keys(['name', 'age', 'addr'])
print(stu_info.values()) #获取字典里面所有的value
# dict_values(['王志华', 18, '北京'])

8、循环字典，每次循环的是字典的key

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
#直接循环字典，看看每次循环的是字典的key
for i in stu_info:
    print(i,stu_info[i])

　　循环字典，每次循环的是字典的key，也可以打印出对应的value值

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
#直接循环字典，看看每次循环的是字典的key
for i in stu_info:
    # print(i,stu_info[i])
    s = " %s => %s" % (i, stu_info.get(i))
    print(s)

7 # name => 王志华
8 #  age => 18
9 #  addr => 北京

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
print(stu_info.items())

for k,v in stu_info.items():
    print(" %s => %s" %(k,v))

9、判断key是否存在

stu_info = {"name": "王志华", "age": 18, "addr": "北京"}
print('name' in stu_info) #判断key是否存在
print('name' in stu_info.keys())#判断key是否存在