Pyhton basic data types V (supplemental)

1. Content Today

1. The underlying data type of supplement
2. Convert between data types
3. Common pit
4. Advanced coding

2. Review yesterday

1. id is ==
   • id: acquiring an object memory address; IS: whether the same memory address; ==: whether the data is the same
2. Code block: a file, interactive command line is a block of code
3. Caching code block
   • Advantages: improve performance, save space
   • A cache mechanism in the same block of code (string resides mechanism)
     • All figures, bool, almost all of the strings
   • Caching mechanism in different code blocks (small data pool)
     • -5 ~ 256 int, bool, string meet certain rules
4. Collection: Role: List de-duplication, relationship test
5. Shades copy:
   • Shallow copy: open up a new space objects stored copy of the (lists, dictionaries) in memory, but all the elements inside the object with the copy inside a shared object
   • Deep copy

3. The specific content

1. Data type of supplement

   #str
   #首字母大写：
   s = 'xiaoshuo'
   s1 = s.capitalize()
   print(s1)
   
   #每个单词首字母大写
   s1 = s.title()
   print(s1)
   
   #大小写互换
   s1 = s.swapcase()
   print()
   
   #统计出现的次数
   s1 = s.count('o')
   print(s1)
   
   #查找
   print(s.find('o')) #find 查找不到返回-1
   print(s.index('o'))#index 查找不到就报错
   
   
   #list
   li = list('8765432') #迭代定义的方式
   print(li)
   
   #统计
   print(li.count('8'))
   
   #查看索引
   print(li.index('8'))
   
   #反转
   li.reverse()
   print(li)
   
   #排序
   li.sort()   #升序
   li.sort(reverse = True)  #降序
   print(li)
   
   
   #tuple
   tu = tuple('123456') #迭代定义元组
   
   #统计
   print(tu.count('1'))
   
   #查找索引
   print(tu.index('1'))
   
   
   #dict
   dic = dict(k1 = 1,k2 = 2, k3 = 3)
   print(dic)
   
   #随机删除：
   dic.popitem()
   python3.6版本之后，默认删除最后个键值对
   python3.5版本以前，随机删除
   
   #批量创建字典：
   dic = {}
   dic1 = dic.fromkeys('qwert',[1234])
   #第一个参数可迭代对象
   #第二个参数时每个键对应的值---用的都是痛一个内存地址
   
   
   #set
   s = set('12345')  #迭代定义方式
   print(s)

2. Basic data type conversion

   #数据类型转换：
    #字符串转化数字的时候必须都是十进制数
     #字符串转列表：
        print(s.split())
     #列表转换字符串
        print(''.join(li))
     #除字典外，数据类型之间可以直接互相转换
   
   
   #基础数据类型分类：
    str;int;bool;tuple;list;dict;set
   #有序
    str;int;bool;tuple;list
   #无序
    dict;set
   #可变
    list;dict;set
   #不可变
    str;int;boo;tuple
   #访问方式
    #直接访问
        int;bool;set
     #顺序访问
        list;tuple;set
     #键访问
        dict    

3. Common pit

   1. List
      • According to the index cycle to delete list elements when you want to delete in reverse order, otherwise the result is not what you want
   2. dictionary
      • Dictionary can not change the size of the dictionary at the time for the cycle
      • If you want to delete the data cycle, we need to define a list of elements within the dictionary list to delete the cycle

4. Advanced coding

   encode()  #编码
   decode()  #解码
   #不同的密码本之间不能相互识别
   #数据在内存中全部是以Unicode编码的，但是当你的数据用于网络传输或者存储到硬盘中，必须是以非Unicode编码的（utf-8，gbk等）
   #用什么编码集编码，就用什么编码集解码