Python基础【day03】：字典（一）

本节内容

简述
语法
字典的使用
字典内置方法

一、简述

字典是Python中的又一种数据结构，它是通过key-value的数据类型，跟我们小时候用的新华字典差不多，通过key去访问value

二、语法

stu_info = {

    "xiedi":28,

    "liuhailin":27,

    "daiqiao":30,

    "hanwenhai":25,

    "chenqun":38

}

2、特性

①字典是无序的

②字典是通过key去访问value（元素不存在重复）

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

#问通过key值访问对应的元素
>>> stu_info["chenqun"]

38

>>>

三、字典的使用

1、增加

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}
>>> stu_info["chenqun"]

38
#新增

>>> stu_info["luoahong"]=32

>>> stu_info

{'hanwenhai': 25, 'daiqiao': 30, 'luoahong': 32, 'chenqun': 38, 'xiedi': 28, 'liuhailin': 27}

2、修改

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

#修改"xiedi"对应的value值，由28改为29
>>> stu_info["xiedi"]=29

#输出
>>> stu_info

{'hanwenhai': 25, 'daiqiao': 30, 'chenqun': 38, 'xiedi': 29, 'liuhailin': 27}

3、删除(del、pop、popitem)

del

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

>>> del stu_info["chenqun"]

#结果输出
>>> stu_info

{'hanwenhai': 25, 'daiqiao': 30, 'xiedi': 29, 'liuhailin': 27}

特别提醒：如果是del stu_info的话，则是删除stu_info这个变量

pop(k)

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

#删除时给出提示
>>> stu_info.pop("liuhailin")

27

#输出结果
>>> stu_info

{'hanwenhai': 25, 'daiqiao': 30, 'chenqun': 38, 'xiedi': 28}

popitem()

随机删除字典中的一个元素

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

#随机删除的元素
>>> stu_info.popitem()

('hanwenhai', 25)

#输出结果
>>> stu_info

{'daiqiao': 30, 'chenqun': 38, 'xiedi': 28, 'liuhailin': 27}

4、查找

key值在字典中存在

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

>>> "chenqun" in stu_info

True

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

>>> stu_info.has_key("daiqiao")　　##标准用法,在Python3和Python2.7都可以用

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

AttributeError: 'dict' object has no attribute 'has_key'

以上这种用法，在Python3和Python2.7都可以用，但是下面这种情况只能在Python2.7上用，Python3已经废除了

get(k)

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

#存在则返回对应的value
>>> print(stu_info.get("daiqiao"))

30

>>> print(stu_info.get("hanwenhai"))

25

通过k获取value

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

#存在key返回value
>>> stu_info["liuhailin"]

27

#不存在key提示报错
>>> stu_info["luoahong"]

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

KeyError: 'luoahong'

小结：get(k)不存在key值，则返回None，通过key直接访问会报错，所以建议推荐用get(k)这个方法获取value

5、多级字典嵌套及操作

av_catalog = {

"欧美":{

"www.youporn.com": ["很多免费的,世界最大的","质量一般"],

"www.pornhub.com": ["很多免费的,也很大","质量比yourporn高点"],

"letmedothistoyou.com": ["多是自拍,高质量图片很多","资源不多,更新慢"],

"x-art.com":["质量很高,真的很高","全部收费,屌比请绕过"]

},

"日韩":{

"tokyo-hot":["质量怎样不清楚,个人已经不喜欢日韩范了","听说是收费的"]

},

"大陆":{

"1024":["全部免费,真好,好人一生平安","服务器在国外,慢"]

}

av_catalog["大陆"]["1024"][1] += ",可以用爬虫爬下来"

print(av_catalog["大陆"]["1024"])

#ouput

['全部免费,真好,好人一生平安', '服务器在国外,慢,可以用爬虫爬下来']

四、字典的内容之方法

1、values()

返回字典中所有value，生成一个列表

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

>>> stu_info.values()
#输出

dict_values([25, 30, 38, 28, 27])

>>>

2、keys()

返回字典中所有key，生成一个列表

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}
>>> stu_info.keys()
#输出结果

dict_keys(['hanwenhai', 'daiqiao', 'chenqun', 'xiedi', 'liuhailin'])

3、setdefault(k,v)

setdefault()表示去取字典中的key，如果取不到，则设置新值，相反如果取到，则返回原有默认值

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}
#设置不存在的key
>>> stu_info.setdefault("luoahong",32)

32

>>> stu_info

#输出结果
{'hanwenhai': 25, 'daiqiao': 30, 'luoahong': 32, 'chenqun': 38, 'xiedi': 28, 'liuhailin': 27}

#设置存在的key
>>> stu_info.setdefault("chenqun",28)

38

#输出结果
>>> stu_info

{'hanwenhai': 25, 'daiqiao': 30, 'luoahong': 32, 'chenqun': 38, 'xiedi': 28, 'liuhailin': 27}

>>>

4、update(dict)

update()是把两个字典合并成一个新的字典，中间有交叉的key，更新替换成新值，没有交叉就直接创建

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

>>> yhd={"luoahong":32,1:2,3:4}

>>> stu_info.update(yhd)

>>> stu_info
#输出

{1: 2, 3: 4, 'chenqun': 38, 'xiedi': 28, 'hanwenhai': 25, 'daiqiao': 30, 'luoahong': 32, 'liuhailin': 27}

注：以后提到更新(update),就是直接原有的字典或者列表上修改，添加(上面的例子就是在stu_info基础上更新的)

5、items()

把字典转换成列表

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

>>> stu_info.items()

dict_items([('hanwenhai', 25), ('daiqiao', 30), ('chenqun', 38), ('xiedi', 28), ('liuhailin', 27)])

6、fromkeys(list,默认值)

初始化一个字典

>>> dict.fromkeys(["xiedi","liuhailin"],1)

{'xiedi': 1, 'liuhailin': 1}

特别提醒:创建多层会有浅copy的作用，所以不建议使用，只需要做了解即可

7、clear()

清空字典

>>> stu_info = { "xiedi":28, "liuhailin":27,"daiqiao":30,"hanwenhai":25,"chenqun":38}

>>> stu_info.clear()

>>> stu_info

{}