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
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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' ]
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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
{}