Python入门之字典dict详细讲解-蒲公英云

Python入门之字典dict详细讲解

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

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)))

2.空字典的定义

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

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))

工厂函数

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

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'])

6.分批赋相同的value值

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

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。

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)

for循环（遍历字典的key值）

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

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)

三、字典的增加

添加不存在的项

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

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)

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)

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)

四、字典的删除

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)

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)

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)

clear清空字典

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

五、字典的查看

查看字典的key值

services = {
```
 'http':80,
 'mysql':3306,
 'smtp':25
```
}
print(services.keys())
查看字典的value值

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

查看字典的key-value值

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

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'))

for迭代

services = {

 'http':80,
 'mysql':3306,
 'smtp':25

}
for k in services:

 print(k,services[k])

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'))