python_字典

ゞ浴缸里的玫瑰 2021-12-11 11:49 361阅读 0赞

字典：

字典取值快，通过key去找

字典是无序的，因为其不是按照顺序进行取值的，是按照key和value进行取值的

1、定义

info=\{\} \#定义空字典

info=\{"name":"zhaozhao","age":23,"sex":"男"\} \#定义字典

2、增加KEY

增加KEY两种方式：

info\["key"\]=value \# 字典该KEY存在改变其值，不存该KEY则增加该KEY

info.setdefault(key,value) \#字典该KEY存在不改变其值，不存该KEY则增加该KEY

info={
        "name":"zhaozhao"}
    info["sex"]=23
    info["name"]="zhaozhao1"
    print(info)

D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py
    {
         'name': 'zhaozhao1', 'sex': 23}

info={
        "name":"zhaozhao"}
    info.setdefault("sex","男")
    info.setdefault("name","zhaozhao2")
    print(info)
    
    D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py
    {
         'name': 'zhaozhao', 'sex': '男'}

3、删除

pop：指定key删除，key不存在会报错

del：指定key删除，key不存在会报错

popitem：随机返回并删除字典中的一对键和值。 如果字典已经为空，却调用了此方法，就报出KeyError异常

info={
        "name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}
    info.pop("name")
    print("pop:",info)
    del  info["sex"]
    print("del:",info)
    info.popitem()
    print("popitem:",info)
    
    
    pop: {
         'sex': '男', 'age': '10', '班级': '1班', '成绩': '90'}
    del: {
        'age': '10', '班级': '1班', '成绩': '90'}
    popitem: {
         'age': '10', '班级': '1班'}

4、字典取值

如果key存在，2者没有什么区别，如果key不存在，info\["key"\]这种方式程序报错，info.get("phone")这种方式返回none

info={
        "name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}
    print(info["name"])
    print(info.get('name'))
    
    print("=========================")
    print(info.get('ab'))
    print(info["ab"])

5、获取key集合，获取value集合

print(info.keys()) \#获取字典所有的key

print(info.values()) \#获取字典所有的value

info={
         "name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}
    print(info.keys())
    print(info.values())
    
    D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py
    dict_keys(['name', 'sex', 'age', '班级', '成绩'])
    dict_values(['zhaozhao', '男', '10', '1班', '90'])

6、判断key是否存在于字典

info.haskey("key") \#python2

key in info \#python3用于这种方式判断key是否存在于字典

info={
          "name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}
    cname='name'
    dname='zhaozhao'
    #key是否在key集合中
    if cname in info.keys():
        print("sucess")
    #value是否在values集合中
    if dname in info.values():
        print("sucess2")
    #key是否在字典中
    if cname in info:
        print("sucess3")

7、一个字典追加另一个字典

info={
          "name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}
    info2={
          "score":"89"}
    info.update(info2)
    print(info)
    
    D:\study\python\test\venv\Scripts\python.exe D:/study/python/test/dd.py
    {
           'name': 'zhaozhao', 'sex': '男', 'age': '10', '班级': '1班', '成绩': '90', 'score': '89'}

8、循环字典值

info={
          "name":"zhaozhao","sex":"男","age":"10","班级":"1班","成绩":"90"}
    for k in info:
        print("%s => %s"%(k,info[k]))
    for k,v in  info.items():
        print("%s => %s"%(k,v))

这两种第一种性能上说快一些，第二种性能弱一些

转载于:https://www.cnblogs.com/xiaokuangnvhai/p/10942346.html