字典的内置方法
【一】字典定义
- 字典中的数据都是 k:v值
- 不支持索引取值,只能支持键值对取值
【二】内置方法
user_data = {'username':'hyt','password':'123'}
【1】查
(1)[键]:如果这个键不存在,就会报错
print(user_data['username']) # hyt
(2).get(键):如果这个键不存在,不会报错并且返回的是 None
print(user_data.get('password')) # 123
print(user_data.get("age")) # None
【2】增加
(1)字典[键]=值
- 这种方式添加键值对,字典中存在该键值对应的值,就会覆盖掉,不存在的话就会新增进去
user_data['age'] = 22
user_data['username'] = 'opp'
user_data['password'] = 999
print(user_data)
{'username': 'opp', 'password': 999, 'age': 22}
(2)setdefault():有返回值并且返回值是加进去的值
user_data = {'username':'hyt','password':'123'}
user_data.setdefault('hobby','music')
print(user_data) # {'username': 'hyt', 'password': '123', 'hobby': 'music'}
(3)update方法
- 第一种方案放一个新的字典
user_data = {'username':'hyt','password':'123'}
data_user = {
'addr':"上海",
"username":"gdy"
}
user_data.update(data_user)
print(user_data) # {'username': 'gdy', 'password': '123', 'addr': '上海'}
- 第二种方案直接放关键字=值
user_data = {'username':'hyt','password':'123'}
user_data.update(age=99)
print(user_data) # {'username': 'hyt', 'password': '123', 'age': 99}
【3】删除
(1)del 删除字典[键]
user_data = {'username':'hyt','password':'123'}
del user_data['username']
print(user_data) # {'password': '123'}
(2)pop(键):将字典中指定的键对于的值弹出
user_data = {'username':'hyt','password':'123'}
print(user_data.pop('username')) # hyt
print(user_data) # {'password': '123'}
(3)clear:清空字典
user_data = {'username':'hyt','password':'123'}
print(user_data.clear())
print(user_data) # {}
(4)popitem: 弹出键值对 默认弹最后的
user_data = {'username':'hyt','password':'123'}
print(user_data.popitem()) # ('password', '123')
print(user_data) # {'username': 'hyt'}
【4】计算元素个数
user_data = {'username':'hyt','password':'123'}
print(len(user_data)) # 2
【5】成员运算
【6】键值对
- 键对
print(user_data.keys()) # dict_keys(['username', 'password'])
print('password' in user_data.keys()) # True
- 值对
print(user_data.values()) # dict_values(['hyt', '123'])
print('666' in user_data.values()) # False
- 键值对
print(user_data.items()) # dict_items([('username', 'hyt'), ('password', '123')])
for key, value in user_data.items(): # username hyt
print(key,value) # password 123
【7】遍历循环
- 可以遍历字典,但是遍历字典出来的是字典的键
- 可以根据遍历的键去取值
user_dict = {'name': "gdy", "age": 18, 1: 2, 2: 3, 3: 4, 4: 5}
for i in user_dict:
print(user_dict[i])
- 可以遍历字典的键对值,根据解压赋值
user_dict = {'name': "gdy", "age": 18, 1: 2, 2: 3, 3: 4, 4: 5}
for key, value in user_dict.items():
print(key, value)
标签:username,内置,方法,123,user,print,password,data,字典
From: https://www.cnblogs.com/wycmjd/p/18111335