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:
