字典的增删改查

Posted 2020-10-22 虫洞小鳗鱼

字典:python中非常重要的数据类型,在python中唯一一个映射的数据类型
数据类型分类

按照数据可变与不可变:
 # 不可变数据类型: int str bool tuple
 # 可变数据类型: list,dict,set

1  键值对
#字典的   key:value# key 是唯一的 且是不可变数据类型  int,str bool tuple

#value:任意数据类型 

2 . 增加数据

dic = {"name":"jin","age":18,"sex":"male"}
#增 dic[\'key\'] = value
# 有key 就覆盖,没有key就添加.
# dic[\'name2\'] = \'依米\'   #没有key name2 就会添加新数据
# print(dic)
# dic[\'name\'] = \'王子\'   #有key name  那么name的值就会被替代
# print(dic)

 

结果:

.setdefault 方法有key不变, 没有key才添加.

dic = {"name":"jin","age":18,"sex":"male"}
#有key不变,没有key才添加.

# dic.setdefault(\'hobby\')  #没有会添加

# print(dic)

# dic.setdefault(\'hobby\',\'开船\')#有就不会变
# print(dic)
# dic.setdefault(\'name\',\'太白\')#有就不会变
# print(dic)

 

结果:

3. 删

.pop 按key删除,有返回值,并且如果没有此key,可设置返回值

dic = {"name":"jin","age":18,"sex":"male"}
ret = dic.pop(\'sex\')
print(ret)
ret = dic.pop(\'sex1\',\'没有此键\')
print(ret)

 

结果:

 

 清空和删除  clear是清空数据 字典还存在 del是删除字典

dic = {"name":"jin","age":18,"sex":"male"}
dic.clear()
print(dic)
# del 删除字典,删除键值对
del dic
print(dic)

 

结果:

.popitem()随机删除一个数据,并产生返回值. 但是python3.6版本以后默认删除最后一个数据

dic = {"name":"jin","age":18,"sex":"male"}
#popitem()  随机删除
ret = dic.popitem()
print(ret)
print(dic)

 

结果:

  4. 改

dic = {"name":"jin","age":18,"sex":"male"}
# 改
#dic[\'key\'] = value
# 有key 就覆盖.
dic["name"]=(1)

结果:

update 将dic的键值对,覆盖,添加到dic2 中,dic不变

dic = {"name":"jin","age":18,"sex":"male"}
dic2 = {"name":"alex","weight":75}
dic2.update(dic)
print(dic)
print(dic2)

 

结果:

5 查
 .get方法通过key找值,如果没有可以加值告知 不添加默认为none

dic = {"name":"jin","age":18,"sex":"male"}
# 查
print(dic[\'name\'])     #输入key 找对应value
print(dic.get(\'name\')) 
print(dic.get(\'name2\',\'没有此键值对\'))
print(dic)

 

 结果:

 

 

a,b能同时赋值,只要后面有两个元素,  int list dict tuple等类型都行

a = 1      #一行代码实现a,b值互换
b = 3
a,b = b,a
print(a,b)
a,b = [\'alex\',\'wusir\']
print(a,b)
a,b = (\'alex\',\'wusir\')
print(a,b)

结果:

  6  找出所有key

dic = {"name":"jin","age":18,"sex":"male"}
for k in dic:
    print(k)
for k in dic.keys():  
    print(k)

 

  7 找出所有values

dic = {"name":"jin","age":18,"sex":"male"}
for v in dic.values():
    print(v)

 

结果:

  8 找出所有键值对;

dic = {"name":"jin","age":18,"sex":"male"}
for k,v in dic.items():
    print(k,v)

for k in dic:
    print(k,dic[k])

 

结果:

 9 字典的嵌套

dic = {
    \'name\':\'金鑫\',
    \'name_list\':[1,2,3,\'李杰\'],
    1:{
        \'python10\':[\'小黑\',\'萌哥\'],
       \'老男孩\':{\'name\':\'oldboy\',\'age\':56}
    }
}
#1,[1,2,3,\'李杰\']追加\'wusir\'
#2, [\'小黑\',\'萌哥\'] 小黑 萌哥中间 插入一个花哥
#3, {\'name\':\'oldboy\',\'age\':56} 添加一个键值对,hobby:男人

dic[\'name_list\'].append(\'wusir\')
print(dic)
l = dic[1][\'python10\']
l.insert(1,\'花哥\')
print(dic)
dic1 = dic[1]
dic2 = dic1[\'老男孩\']
dic2[\'hobby\'] = \'男人\'

 

结果: