python（字典函数/操作）

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gril
  stu["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None
  print (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"))      #True
print (a.has_key("height"))   #False

user = input("账号：")
pwd = input("密码：")
mysql.setdefault(user,pwd)
print mysql
if mysql.has_key(user):
    print ("ok")
else:
    print ("no")