Python之字典的详细介绍及使用示例

一、字典的定义

字典是一个无序的数据集合，使用print输出字典的时候
通常输出的顺序和定义的顺序是不一致的

字典：key - value 键值对
value可以是任意数据类型

s = {
    'linux':[100,99,88],
    'westos':[190,5,5]
}
print(s,type(s))

1、工厂函数

d = dict()			#定义空字典
print(type(d))

d1 = dict(a=1,b=2)	#工厂函数
print(d1,type(d1))

2、字典的嵌套

students = {
    '03113009':{
        'name':'laozhao',
        'age':18,
        'score':80
    },
    '03113010':{
        'name': 'laoyan',
        'age': 30,
        'score': 59
    }
}

print(students['03113010']['age'])

3、定义一个字典的所有key对应的value值是一样的

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

二、字典的特性

• 字典不支持索引
• 字典不支持切片
• 字典的重复和连接无意义

1、成员操作符

d = {
    '1':'a',
    '2':'b'
}

print('2' in d)

2、for循环，默认遍历字典的key值

d = {
    '1':'a',
    '2':'b'
}

for i in d:
    print(i)

d = {
    '1':'a',
    '2':'b'
}

for i in d:
    print(i,d[i])
    
for k,v in d.items():		#遍历key，value值
    print(k,':',v)

三、字典的增加

1、添加一个key-value值

如果key值存在，则更新对应的value值
如果key值不存在，则添加对应key-value

示例：

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

services['mysql'] = 3306		#不存在，添加对应key-value
print(services)

services['http'] = 443			#存在，则更新对应的value值
print(services)

2、添加多个key-value值

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}
services_backup = {
    'https':443,
    'tomcat':8080,
    'http':8080
}

services.update(services_backup)
print(services)

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

services.update(flask=9000,http=8000)
print(services)

3、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,
    'ftp':21,
    'ssh':22
}

services.setdefault('http',9090)
print(services)

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

services.setdefault('oracle',44575)
print(services)

四、字典的删除

1、del

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

del services['http']
print(services)

2、pop删除指定key的key-value

如果key存在，删除，并返回删除key对应的value
如果不存在，报错

示例：

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

item = services.pop('http')
print(item)
print(services)

3、popitem删除最后一个key-value值

示例：

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

item = services.popitem()
print('删除的是:',item)
print(services)

4、清空字典内容

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

services.clear()
print(services)

五、字典的查看

1、查看字典的key值

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

print(services.keys())

2、查看字典的value值

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

print(services.values())

3、查看字典的key-value值

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

print(services.items())

4、查看key的value值

key不存在，默认返回none
key不存在，有default值，则返回default值

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

print(services.get('http'))

5、for循环（迭代）

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

for k,v in services.items():
    print(k,'--->',v)

for k in services:
    print(k,'--->',services[k])

6、get方法获取指定key对应的value

services = {
    'http':80,
    'ftp':21,
    'ssh':22
}

print(services.get('https','key not exist'))