Python入门之字典dict详细讲解

雨点打透心脏的1/2处 2021-12-15 00:15 415阅读 0赞

一、字典的定义

字典是一个无序的数据集合，通常输出的顺序和定义的顺序不一致

1. 字典的创建

users = ['user1','user2']
    passwd = ['123','456']
    print(zip(users,passwd))
    print(list(zip(users,passwd)))
    print(dict(zip(users,passwd)))

![20190704100428990.png][]

2.空字典的定义

s = {}      #空字典
    print(type(s))
    d = dict()      #空字典
    print(d,type(d))

![20190704100524585.png][]

3. 字典格式：key-value键值对

字典的key值是唯一的

s = {
        'westos':[190,521,231],
        'mysql':[100,99,88]
    }
    print(s,type(s))

![20190704100625387.png][]

4. 工厂函数

d1 = dict(a=1,b=2)
    print(d1,type(d1))

![20190704102135861.png][]

5.嵌套

students = {
        '03113009':{
            'name':'laoli',
            'age':39,
            'score':59
        },
        '03113010':{
            'name':'westos',
            'age':18,
            'score':61
        }
    }
    print(students['03113009']['name'])
    print(students['03113010'])

![20190704102246766.png][]

6.分批赋相同的value值

print({}.fromkeys({'1','2'},'000000'))

![20190704102729487.png][]

二、字典的特性

字典不支持索引和切片，字典的重复和连接也是无意义的。

1. 成员操作符

d = {
        '1':'a',
        '2':'b'
    }
    print('1' in d)     #对key进行判定
    print('1' not in d)

![20190704193011461.png][]

2. for循环（遍历字典的key值）

d = {
        '1':'a',
        '2':'b'
    }
    for key in d:
        print(key)

![20190704193142908.png][]

遍历字典

d = {
        '1':'a',
        '2':'b'
    }
    for key in d:           #与下一个作用类似
        print(key,d[key])
     
    for k,v in d.items():
        print(k,v)

![20190704193256264.png][]

三、字典的增加

1. 添加不存在的项

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services)
    services['ftp'] = 21
    print(services)

![20190704193355785.png][]

2. 添加已经存在的项，会更改值

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services)
    services['http'] = 443
    print(services)

![20190704193624262.png][]

3. 添加多个key-value值

如果添加的key-value存在，则只改变键值；不存在的项会直接添加

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    services_backup = {
        'https':443,
        'tomcat':8080,
        'http':8080
    }
    print(services)
    services.update(services_backup)
    print(services)
     
    services.update(flask=9000,http=8000)
    print(services)

![20190704193847409.png][]

4. setdefault添加key值

如果key值存在，不做修改；如果key值不存在，添加对应的key-value

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services)
    services.setdefault('http',9090)
    print(services)
     
    services.setdefault('oracle',44575)
    print(services)

![20190704194348100.png][]

四、字典的删除

1. del删除指定的key-value键值对

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services)
    del services['http']
    print(services)

![20190704194501504.png][]

2. pop删除指定的key的key-value

如果key存在，删除，并返回删除key对应的value；如果key不存在，报错

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    item = services.pop('http')
    print(item)
    print(services)

![20190704195021236.png][]

3. popitem删除最后一个key-value值对

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services)
    item = services.popitem()
    print(services)

![20190704195255797.png][]

4. clear清空字典

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    services.clear()
    print(services)

![20190704195410510.png][]

五、字典的查看

1. 查看字典的key值

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services.keys())

![20190704195551803.png][]

2. 查看字典的value值

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services.values())

![20190704195643888.png][]

3. 查看字典的key-value值

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services.items())

![20190704195733304.png][]

4. 查看key的value值

key不存在，默认返回None；key不存在，有defaulte，则返回defaulte值

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services.get('https'))
    print(services.get('http'))

![20190704195820926.png][]

5. for迭代

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    for k in services:
        print(k,services[k])

![2019070419591194.png][]

6. get方法

如果key值存在，返回；如果不存在，默认返回None，如果需要指定返回值，传值即可

services = {
        'http':80,
        'mysql':3306,
        'smtp':25
    }
    print(services.get('https','key not exist'))
    print(services.get('mysql','key not exist'))

![20190704200023906.png][]

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