一.字典操作
1.往字典中添加键值对
- dict[“key”] = “value”
stu = {"}stu["sex"] = "boy"print (stu) - setdefault（）
stu = {"}stu.setdefault("sex")print (stu) #结果 {'age': '18', 'name': 'zhangsan', 'sex': None}stu = {"}stu.setdefault("sex","boy")print (stu) #结果 {'age': '18', 'name': 'zhangsan', 'sex': 'boy'}
2.替换字典中指定键的值
- dict[“key”] = “value”
stu = {"name":"zhangsan","age":18,"sex":"boy"}#替换值boy为grilstu["sex"] = "girl"print (stu)
3.update（）一个字典所有项追加到另一个字典里
a = {"name":"zhangsan","sex":"boy"}b = {"age":18}a.update(b) #往字典a中追加字典b的内容print (a)print (b)
4.字典取值
- get（）函数 –> 当提取的键不存在时，不会报错，为空
a = {"name":"zhangsan","sex":"boy"}print (a.get("name"))#当取的键不存在时，不报错，返回值为Noneprint (a.get("age"))#示例"""dic = {"name1":"zhangsan","age":{"age1":"18","age2":20},"name2":"lisi","name3":"wangwu"}""" - dict[“key”]
a = {"name":"zhangsan","sex":"boy"}print (a["name"])
5.keys（）从字典中取出所有键
- 不能通过在括号中输入键来取键值
- 返回的是一个键列表
a = {"name":"zhangsan","sex":"boy","age":18}print (a.keys()) #返回所有键列表
6.values（） 从字典中取出所有值
- 返回的是一个值列表
a = {"name":"zhangsan","sex":"boy","age":18}print (a.values()) #返回所有值列表
7.del 删除键值对
a = {"name":"zhangsan","sex":"boy","age":18}del a["name"]print (a) #结果中"name":"zhansan"该键值对全部被删除
8.pop（）删除键值对
- 括号中必须为键且不能为空
- 返回值为删除键的值
a = {"name":"zhangsan","sex":"boy","age":18}value = a.pop("name")print (value) #返回值为"zhangsan"print (a) #字典a中的"name":"zhangsan"键值对被删除
9.popitem（）随机删除字典第一个键值对
- 并返回该键值对的元组
a = {"name":"zhangsan","sex":"boy","age":18}b = a.popitem()print (b) #返回值为包含被删除的键值对的一个元组print (a) #字典a中的某个键值对被删除
10.clear（）清空字典中的键值对
- 没有返回值
- 原字典为空字典{}
a = {"name":"zhangsan","sex":"boy","age":18}a.clear()print (a)
11.copy（）复制创建字典
a = {"name":"zhangsan","sex":"boy","age":18}b = a.copy()print (b) #b是a复制出来的字典
12.has_key（）检查字典是否有指定的键，有结果为 True，没有结果为 False
a = {"name":"zhangsan","sex":"boy","age":18}print (a.has_key("age")) #Trueprint (a.has_key("height")) #False
user = input("账号：")pwd = input("密码：")mysql.setdefault(user,pwd)print mysqlif mysql.has_key(user): print ("ok")else: print ("no")
