字典
字典是python中唯一的映射类型&＃xff0c;采用键值对&＃xff08;key-value&＃xff09;的形式存储数据。python对key进行哈希函数运算&＃xff0c;根据计算的结果决定value的存储地址&＃xff0c;所以字典是无序存储的&＃xff0c;且key必须是可哈希的。可哈希表示key必须是不可变类型&＃xff0c;如&＃xff1a;数字、字符串、元组。
字典(dictionary)是除列表意外python之中最灵活的内置数据结构类型。列表是有序的对象结合&＃xff0c;字典是无序的对象集合。两者之间的区别在于&＃xff1a;字典当中的元素是通过键来存取的&＃xff0c;而不是通过偏移存取。
可变数据类型&＃xff1a;列表list&＃xff0c;字典dict 又叫不可哈希
不可变数据类型&＃xff1a; 元祖&＃xff0c;bool值&＃xff0c;数字int&＃xff0c;字符型str 本身不可变&＃xff0c;又叫可哈希
key 键&＃xff0c;必须是不可变类型&＃xff0c;可哈希
value 值&＃xff0c;任意数据类型
创建空字典使用 { }
字典dict优点&＃xff1a;
1&＃xff0c;用二分法查询&＃xff0c;查询速度快
2&＃xff0c;储存大量的关系型数据
字典dick特点&＃xff1a;
字典dict是无序的。&＃xff08;3.5及之前的字典dict是无序的&＃xff09;
简写为dic
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18,&＃39;num&＃39;:[1,2,3,&＃39;alex&＃39;],&＃39;s1&＃39;:{&＃39;xiao&＃39;:&＃39;han&＃39;,&＃39;gh&＃39;:[1,2,3,4]},&＃39;qq&＃39;:123
}
print(dic)
结果 {&＃39;name&＃39;: &＃39;xiaoming&＃39;, &＃39;age&＃39;: 18, &＃39;num&＃39;: [1, 2, 3, &＃39;alex&＃39;], &＃39;s1&＃39;: {&＃39;xiao&＃39;: &＃39;han&＃39;, &＃39;gh&＃39;: [1, 2, 3, 4]}, &＃39;qq&＃39;: 123}
增&＃xff0c;两种方法&＃xff08;注意与列表list区别&＃xff09;
直接加&＃xff0c;如果没有对应键值&＃xff0c;则直接加在后面。如果有对应键值&＃xff0c;则进行覆盖。
dic1 &＃61;{&＃39;name&＃39;:&＃39;xiaojun&＃39;}
dic1[&＃39;height&＃39;] &＃61; 180
print(dic1)
dic.setdefault(&＃39;&＃39;) 形式&＃xff0c;有对应键值&＃xff0c;则不做任何修改。没有对应键值&＃xff0c;后面默认加None
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18,&＃39;num&＃39;:[1,2,3,&＃39;alex&＃39;],&＃39;s1&＃39;:{&＃39;xiao&＃39;:&＃39;han&＃39;,&＃39;gh&＃39;:[1,2,3,4]},&＃39;qq&＃39;:123
}
dic.setdefault(&＃39;weighe&＃39;)print(dic)
dic.setdefault(&＃39;weighe&＃39;&＃xff0c;180) 另一种形式
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18,&＃39;num&＃39;:[1,2,3,&＃39;alex&＃39;],&＃39;s1&＃39;:{&＃39;xiao&＃39;:&＃39;han&＃39;,&＃39;gh&＃39;:[1,2,3,4]},&＃39;qq&＃39;:123
}
dic.setdefault(&＃39;weighe&＃39;&＃xff0c;180)print(dic)
结果 {&＃39;name&＃39;: &＃39;xiaoming&＃39;, &＃39;age&＃39;: 18, &＃39;num&＃39;: [1, 2, 3, &＃39;alex&＃39;], &＃39;s1&＃39;: {&＃39;xiao&＃39;: &＃39;han&＃39;, &＃39;gh&＃39;: [1, 2, 3, 4]}, &＃39;qq&＃39;: 123, &＃39;weighe&＃39;: 180}
删&＃xff0c;
dic.pop(‘’)直接删
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
dic.pop(&＃39;age&＃39;)
print(dic)
有返回值&＃xff0c;返回被删除的键值
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
s &＃61; dic.pop(&＃39;age&＃39;)
print(s)
结果18
可设置返回值&＃xff0c;如果没有对应的被删键值&＃xff0c;返回自己设定的值&＃xff0c;就是下面的‘不错’
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
s &＃61; dic.pop(&＃39;aa&＃39;,&＃39;不错&＃39;) #如果aa变成name&＃xff0c;则返回小明
print(s)
结果 不错
dic.popltem()形式&＃xff0c;随机删除一个&＃xff0c;3.6版本默认删除最后一个dic &＃61; {&＃39;aa&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
dic.popitem()
print(dic)结果 {&＃39;aa&＃39;: &＃39;xiaoming&＃39;}
dic &＃61; {&＃39;aa&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18} #这种&＃xff0c;有返回值
print(dic.popitem())
结果 (&＃39;age&＃39;, 18)
清空列表
dic &＃61; {&＃39;aa&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
dic.clear()print(dic)结果 {}
改
直接改
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
dic[&＃39;age&＃39;] &＃61; 16
print(dic)
dic1.update(dic)覆盖增加&＃xff0c;把dic覆盖增加到dic1中&＃xff0c;
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
dic1 &＃61;{&＃39;name&＃39;:&＃39;xiaojun&＃39;,&＃39;height&＃39;:180}
dic1.update(dic)
print(dic1)
dic和dic1中对应的键&＃xff0c;则用dic的键值覆盖dic1的&＃xff0c;dic没有与dic1中对应的减&＃xff0c;则直接加入dic1中&＃xff0c;dic1中多的键值&＃xff0c;则直接保留
结果{&＃39;name&＃39;: &＃39;xiaoming&＃39;, &＃39;height&＃39;: 180, &＃39;age&＃39;: 18}
查
dic[&＃39;直接查&＃39;]直接查&＃xff0c;没有会报错
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
print(dic["name"])
dic.get(&＃39;high&＃39;,&＃39;设置返回的值‘&＃xff09;
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
print(dic.get("high","默认返回值") ) # 没有可以返回设定的返回值
#print(dic.get(&＃39;high&＃39;)) 默认返回None
只打印键
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18} &＃61; dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;&＃xff1b;18}
for i in dic: &＃61; for i in dic.keys():print(i) &＃61; print(i)
结果 name 结果 name
age age
只打印值
dic &＃61; {&＃39;name&＃39;:&＃39;xiaoming&＃39;,&＃39;age&＃39;:18}
for i in dic.values():print(i)结果 xiaoming18
a &＃61; 1
b &＃61; 2
a,b &＃61; b,a
print(a,b)
items 同时打印keys 和 valuces
dic &＃61; {&＃39;k1&＃39;: "v1", "k2": "v2", "k3": [11,22,33]}
for i in dic.items():print(i)
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