Python——字典

一、字典特性介绍

字典在 Python 中极为重要，是属于映射类型的数据结构。字典有⼀对⼉⼤括号组成 {} , 字典内的元素都是成对⼉出现的 {"a":1} , 他们⽤英⽂的冒号( : )隔开, 左边叫做键(key),右边的叫值(value), 通常叫做键值对⼉。每个元素⽤英⽂的逗号 ( , ) 隔开{"a": 1, "b": 2}

二、创建字典

创建字典可以使⽤⼀对⼉⼤括号，也可以使⽤ dict()

In [1]: d1 = {}In [2]: type(d1)
Out[2]: dictIn [3]: d2 = dict()In [4]: type(d2)
Out[4]: dict

三、字典的 key 和 value

1、字典的 key

在⼀个字典中，key 不允许有重复

In [5]: {"a":1,"a":10}
Out[5]: {'a': 10}

且必须是 python 中不可变的数据类型如：整型浮点型布尔值字符串元组

In [6]: {1: "整型", 1.1: "浮点型", False: "布尔值", "abc":"字符串", (1,2): "...: 元组" }
Out[6]: {1: '整型', 1.1: '浮点型', False: '布尔值', 'abc': '字符串', (1, 2): '元组'}

最常⽤的是字符串，因为⽐较容易有语意，易读

In [7]:  {"user": "shark", "age": 18}
Out[7]: {'user': 'shark', 'age': 18}

扩展：python 中认为 1 和 True , 0 和 False 的值是相等的但不是⼀个对象，因为它们的 id 不同

In [8]: {1: "整型", True: "布尔型"}
Out[8]: {1: '布尔型'}In [9]: {True: "布尔型", 1: "整型"}
Out[9]: {True: '整型'}

2、字典中的 value

字典中的 value 可以是 Python 中任意的⼀个数据对象：整型、浮点型、布尔值、字符串、列表、元组、字典、函数对象等

In [10]: {'port': 3306, "height": 1.81, 'stat': True,"name": "dbserver"}
Out[10]: {'port': 3306, 'height': 1.81, 'stat': True, 'name': 'dbserver'}In [11]: {"mysql-01": {...:     "cpu":4,...:     "memroy":[4066,4096]...:     }...: }
Out[11]: {'mysql-01': {'cpu': 4, 'memroy': [4066, 4096]}}

函数对象

In [12]: def foo():...:     print("hello")...: In [13]: {"1":foo}
Out[13]: {'1': <function __main__.foo()>}

四、获取字典中 key 和 value

1、检查字典中是否存在某个 key

可以使⽤ in 关键字

In [14]: dic_map = {...:     "Manufacturer": "manufacturer",...:     "Product Name": "pod_name",...:     "Serial Number": "sn"...: }In [15]: dic_map
Out[15]: 
{'Manufacturer': 'manufacturer','Product Name': 'pod_name','Serial Number': 'sn'}In [16]: "Manufacturer" in dic_map
Out[16]: TrueIn [17]: "Manufactur" in dic_map
Out[17]: FalseIn [18]: line = '\tManufacturer: Alibaba Cloud'In [19]: line.strip().split(': ')
Out[19]: ['Manufacturer', 'Alibaba Cloud']In [20]: k = line.strip().split(': ')[0]In [21]: k in dic_map
Out[21]: True

2、使⽤ [] 获取指定 key 的 value

In [22]: dic_map['Manufacturer']
Out[22]: 'manufacturer'

这种⽅式是⾮常的⾼效做法，推荐使⽤。但是有个问题，假设获取字典中不存在的 key 的值

3、使⽤字典的 get() ⽅法

In [27]: dic_map.get('Manufacturer')
Out[27]: 'manufacturer'In [28]: v = dic_map.get('Manufacturer')In [29]: v
Out[29]: 'manufacturer'In [30]: v = dic_map.get('Manufacturerr')In [31]: vIn [32]: type(v)        # key 不存在字典中，则返回 None
Out[32]: NoneTypeIn [33]: v = dic_map.get('Manufacturerr', 'key not in')    # key 不存在，返回自定义值In [34]: v
Out[34]: 'key not in'

4、循环字典的 key 和 value

字典对象的 items() ⽅法会获取到字典的 key 和 value, 它是⼀个可迭代对象

In [9]: for i in dic_map.items():...:     print(i)...: 
('Manufacturer', 'manufacturer')
('Product Name', 'pod_name')
('Serial Number', 'sn')In [10]: for i in dic_map.items():...:     k, v = i...:     print(k , v)...: 
Manufacturer manufacturer
Product Name pod_name
Serial Number sn

5、向字典中添加键值对

方式一：[]

In [12]: info = {}In [13]: info["cpu"] = 4In [14]: info["memory"] = [4096,4096]In [15]: info
Out[15]: {'cpu': 4, 'memory': [4096, 4096]}

字段映射

In [16]: dic_map
Out[16]: 
{'Manufacturer': 'manufacturer','Product Name': 'pod_name','Serial Number': 'sn'}In [17]: li = ['Manufacturer: Alibaba Cloud',...:     'Product Name: Alibaba Cloud ECS',...:     'Version: pc-i440fx-2.1',...:     'Serial Number: 0f7e3d86-7742-4612-9f93-e3a9e4754157']In [18]: prod_info = {}In [19]: for line in li:...:     print(line)...: 
Manufacturer: Alibaba Cloud
Product Name: Alibaba Cloud ECS
Version: pc-i440fx-2.1
Serial Number: 0f7e3d86-7742-4612-9f93-e3a9e4754157In [20]: for line in li:...:    print( line.split(': '))...: 
['Manufacturer', 'Alibaba Cloud']
['Product Name', 'Alibaba Cloud ECS']
['Version', 'pc-i440fx-2.1']
['Serial Number', '0f7e3d86-7742-4612-9f93-e3a9e4754157']In [22]: for line in li:...:    k, v = line.split(': ')...:    if k in dic_map:...:        new_k = dic_map[k]...:        print(new_k,v)...: 
manufacturer Alibaba Cloud
pod_name Alibaba Cloud ECS
sn 0f7e3d86-7742-4612-9f93-e3a9e4754157In [23]: for line in li:...:    k, v = line.split(': ')...:    if k in dic_map:...:        new_k = dic_map[k]...:        prod_info[new_k] = v        # 获取的⼀个字典的值作为另⼀个字典的键...: In [24]: prod_info
Out[24]: 
{'manufacturer': 'Alibaba Cloud','pod_name': 'Alibaba Cloud ECS','sn': '0f7e3d86-7742-4612-9f93-e3a9e4754157'}

方式二：update

In [25]: disk = {"disk": [10240]}In [26]: info = {}In [27]: info.update(disk)In [28]: info
Out[28]: {'disk': [10240]}In [29]: info.update({'cpu':4})In [30]: info
Out[30]: {'disk': [10240], 'cpu': 4}In [31]: info['disk']
Out[31]: [10240]In [32]: info['disk'][0]
Out[32]: 10240

6、字典的编程之道：⽤字典实现 case 语句

In [45]: !vi some.py     #程序
data = {                   "0": "zero","1": "one","2": "two","q": "quit"
}while True:arg = input(">>:")v = data.get(arg, "nothing")if v == "quit":breakprint(v)In [46]: %run some.py    #执⾏程序
>>:1
one
>>:2
two
>>:3
nothing
>>:4
nothing
>>:q