python字典操作

1、定义字典

>>> d1 = {                         //key-value的格式

    "student1":"xiaoming",

    "student2":"zhangsan",

    "student3":"lisi" 

     }

2、查看

>>> print(d1["student1"])      //在已知有此key的情况下使用，在没有此key时会报错

xiaoming

>>> print(d1.get("student2"))   //get方法不会报错

zhangsan

>>> print(d1.get("student1"))

None

3、修改key的值

>>> print(d1["student1"])

xiaoming

>>> d1["student1"] = "XiaoMing"         //如果存在则修改，不存在则添加

>>> print(d1["student1"])

XiaoMing

4、删除

>>> del d1["student1"]

>>> print(d1)

{'student2': 'zhangsan', 'student3': 'lisi'}

5、判断字典里有没有某数据

>>> print("student1" in d1)

False

6、多级字典的嵌套

>>> d2 = {

    "weibo":{

        "guomao":["wilson","david","lucia"],

        "bagou":["zhangsan","wangwu","lisi"]},

    "xindongfang":{

        "yuquan":["piter","alen","cc"],

        "wukesong":["shenyang","lidong","wangwei"]}

    }

7、修改嵌套菜单中的值

>>> print(d2["weibo"]["guomao"])            

['wilson', 'david', 'lucia']              //修改之前

>>> d2["weibo"]["guomao"][1] = "大卫"

>>> print(d2["weibo"]["guomao"])

['wilson', '大卫', 'lucia']              //修改之后

8、打印字典中的所有值

>>> print(d2.values())

9、打印字典中所有的key

>>> print(d2.keys())

10、如果字典中存在此键则返回，不存在则创建

>>> print(d2)

{'weibo': {'guomao': ['wilson', '大卫', 'lucia'], 'bagou': ['zhangsan', 'wangwu', 'lisi']}, 'xindongfang': {'yuquan': ['piter', 'alen', 'cc'], 'wukesong': ['shenyang', 'lidong', 'wangwei']}}

>>> d2.setdefault("weibo",{"xinhua":["aa","bb","cc"]})

{'guomao': ['wilson', '大卫', 'lucia'], 'bagou': ['zhangsan', 'wangwu', 'lisi']}

>>> d2.setdefault("yingfu",{"xinhua":["aa","bb","cc"]})

{'xinhua': ['aa', 'bb', 'cc']}

>>> print(d2)

{'weibo': {'guomao': ['wilson', '大卫', 'lucia'], 'bagou': ['zhangsan', 'wangwu', 'lisi']}, 'xindongfang': {'yuquan': ['piter', 'alen', 'cc'], 'wukesong': ['shenyang', 'lidong', 'wangwei']}, 'yingfu': {'xinhua': ['aa', 'bb', 'cc']}}

11、合并两个字典，如果字典中有相同的key则更新，没有则添加

>>> d1

{'student2': 'zhangsan', 'student3': 'lisi'}

>>> d3 = {"student2":"AAAA","BBBBB":"CCCCC",1:2}

>>> d1.update(d3)

>>> print(d1)

{'student2': 'AAAA', 'student3': 'lisi', 'BBBBB': 'CCCCC', 1: 2}

12、把字典转换成列表

>>> print(d1.items())

dict_items([('student2', 'AAAA'), ('student3', 'lisi'), ('BBBBB', 'CCCCC'), (1, 2)])

可以循环打印

>>> for k,v in d1.items():

...   print(k,v)

... 

student2 AAAA

student3 lisi

BBBBB CCCCC

1 2

13、字典的循环

>>> for i in d1:       

...   print(i)         //只打印key

... 

student2

student3

BBBBB

1

>>> for i in d1:

...   print(i,d1[i])        //把i当做key传入到字典中查询

... 

student2 AAAA

student3 lisi

BBBBB CCCCC

1 2

14、for k,v in d1.items():和for i in d1:print(i,d1[i])的区别

第二种方式比较高效，因为第一种方式先把字典转换为列表，在数据量大的情况下，会导致资源的浪费。