字典的增删改查和嵌套

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

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:

原文地址：https://www.cnblogs.com/wzbk/p/8352213.html