18.07.06

标签：查询   键值对   tde   默认值   年龄   限制   直接   重复   default   

字典

dict{}:括起来的键值对是字典.{key:value}

字典中的key必须是可哈希的(不可变的).value没有限制.

整数.字符串.元组是不可变的,列表是可变的.

  增:

例:  

dic={"A":"a"}
dic["B"]="b"
print(dic)     ==<{‘A‘: ‘a‘, ‘B‘: ‘b‘}>

 例:  如果key重复了,value会被替换.

dic={"A":"a"}
dic["B"]="b"
dic["B"]="2"   #赋值
print(dic)     ==<{‘A‘: ‘a‘, ‘B‘: ‘2‘}>

setdefault 如果字典中包含这个key则不再继续保存.

例:

dic={"A":"a"}
dic.setdefault("C","c")
print(dic)    ==<"A":"a","C":"c">

dic.setdefault("C",3)
print(dic)    ==<"A":"a","C":"c">

  删除:

(1)pop(key)

例:

dic={"A":"a","B":"b","C":"c"}
dic.pop("A")
print(dic)    ==<{‘B‘: ‘b‘, ‘C‘: ‘c‘}>

例:

dic={"A":"a","B":"b","C":"c"}
ret=dic.pop("A")
print(ret)    ==<a>

(2)del dic[key]

例:

dic={"A":"a","B":"b","C":"c"}
del dic["B"]
print(dic)    ==<{‘A‘: ‘a‘, ‘C‘: ‘c‘}>

(3)popitem()  随机删除

例:

dic={"A":"a","B":"b","C":"c"}
ret=dic.popitem()
print(ret)    ==<(‘C‘, ‘c‘)>
print(dic)    ==<{‘A‘: ‘a‘, ‘B‘: ‘b‘}>

(4)clear  清空

例:

dic={"A":"a","B":"b","C":"c"}
dic.clear()
print(dic)     ==<{}>

  修改:

(1)可以用key直接修改.

例:

dic1={"A":1,"D":"d","C":3}

dic1["C"]=dic1["C"]-2
print(dic1)     ==<{‘A‘: 1, ‘D‘: ‘d‘, ‘C‘: 1}>

(2)字典1.update(字典2) 把字典2添加的字典1中,如果字典2中key和字典1中的key重复则替换vlaue,如果不重复,则添加.

例:

dic={"A":"a","B":"b","C":"c"}
dic1={"A":1,"D":"d","C":3}

dic.update(dic1)
print(dic)     ==<{‘A‘: 1, ‘B‘: ‘b‘, ‘C‘: 3, ‘D‘: ‘d‘}>

   查找:

(1)用key直接查找

例:

dic={"及时雨":"宋江","小李广":"花荣","易大师":"剑圣"}

print(dic["易大师"])   ==<剑圣>

(2)get 如果key不存在则返回None,如果不想找回None可以添加一个默认值.  key存在则返回value

例:

dic={"及时雨":"宋江","小李广":"花荣","易大师":"剑圣"}
print(dic.get("李光","默认值"))    ==<默认值>

(3)setdefault  先判断字典中有没有key,如果没有则添加.  再用这个key去字典中查询,返回查到的结果.

例:

dic={"及时雨":"宋江","小李广":"花荣"}
ret=dic.setdefault("诺手","诺克")
print(ret)     ==<诺克>    #查询
print(dic)     ==<{‘及时雨‘: ‘宋江‘, ‘小李广‘: ‘花荣‘, ‘诺手‘: ‘诺克‘}>    #添加 

 相关操作:

(1)keys  返回所有的key  结果像集合像列表但不是列表  可以进行迭代循环.

 例:

dic={"及时雨":"宋江","小李广":"花荣"}
print(dic.keys())    ==<dict_keys([‘及时雨‘, ‘小李广‘])>

for s in dic.keys():
    print(s)       
==<及时雨
   小李广>

(2)values 返回所有的value值   结果像集合像列表但不是列表  可以进行迭代循环.

例:

dic={"及时雨":"宋江","小李广":"花荣"}
print(dic.values())     ==<dict_values([‘宋江‘, ‘花荣‘])>
for s in dic.values():
    print(s)     
==<宋江
   花荣>

(3)items  返回所有key,value值     结果像列表但不是列表,列表中的元素是元组.

例:

dic={"及时雨":"宋江","小李广":"花荣"}
print(dic.items())      ==<dict_items([(‘及时雨‘, ‘宋江‘), (‘小李广‘, ‘花荣‘)])>#键值对
for s in dic.items():
    print(s)          
==<(‘及时雨‘, ‘宋江‘)
   (‘小李广‘, ‘花荣‘)>
    print(s[0])
==<及时雨
   小李广>
    print(s[1])
==<宋江
   花荣>
根据解构的一种算法:

dic={"及时雨":"宋江","小李广":"花荣"}
for k,v in dic.items():
    print(k)    
==<及时雨
   小李广>
    print(v)
==<宋江
   花荣>

解构,解包

例:

a,b=1,2
print(a)   ==<1>
print(b)   ==<2>

例:

a=1,2  ==>  a=(1,2)
print(a)   ==<(1,2)>

例:

a,b=(1,2)
print(a)    ==<1>

 字典的嵌套

例:

dic={"name":"汪峰",
     "age":58,
     "wife":{"name":"章子怡",
             "age":37,
             "salar":1800000},
     "children":[{"name":"老大","age":18},
                {"name":"老二","age":7}]}
print(dic["wife"]["salar"])          ==<1800000>
print(dic["children"][1]["age"])     ==<7> #第二个孩子的年龄

18.07.06

标签：查询   键值对   tde   默认值   年龄   限制   直接   重复   default   

原文地址：https://www.cnblogs.com/gxj742/p/9275640.html