20/01/26 Python learning the basics (10)

Object persistence

• Application scenario
  serialization and deserialization of: storing a result of the current data being evaluated, or progress to a certain physical state not connected; future in a particular context restore the data stored in the memory to go.
• technology

1. Flat file

• Text File

  scores=[99,88,77,66]
  def write_score():
  	with open('datalist.txt','w',ecoding='utf8') as f:
  		f.write(string(scores))
  	print('文件写入完成...')
  def read_score:
  	with open('datalist.txt','r',ecoding='utf8') as f:
  		lst=eval(f.read())  #将传递的字符串转换为python表达式 
  	```
  	
  

2. pickle
   encapsulating a series of methods interfaces, python any original type object can be serialized into a string file or local

• Serialized as a string

  import pickle
  person={'name':'Tom','age':20}
  s=pickle.dumps(person) #将python类型序列化为字节字符串
  p=picle.loads(s) #从字符串反序列化对象（保留类型特征）
  

• Serialized object to a file

  pickle.dump(person,open('pickle_db','wb'))   #.dump(obj,file)
  p=pickle.load(open('pickle_db','rb'))  #.load(file)
  

3. shelve - wherein: a plurality of objects are stored in a file, similar to the form dictionary tables keys to access different object

   import shelve
   scores=[99,88,77]
   student={'name':'Tom','age':20}
   db=shelve.open('shelve_student')
   db['s']=student
   db['scores']=scores
   # 调用
   db['s']
   # 删除文件
   del db['scores']
   

4. database

5. SNAKE

String

• Outline
  • Types of
    • str string
    • bytes bytes
    • byte array bytearray
  • Character Encoding Architecture
    • Character Set: assign a code to a character to represent in memory
    • Encoding Encoding: conversion character to the original byte form
    • Decoding Decoding: converting raw byte encoding name based on the character of the process
  • String is stored
    • Encoding only acts on a storage medium or intermediate conversion
    • Always stored in memory after the decoded text
• Character Encoding
  • The ASCII American Standard Code for Information Interchange (number / letter / punctuation / line feed ...)
    stored in a byte 0-127
  • Latin-1
    is stored in a byte 128-255
  • UTF-8 guarantee compatibility while minimizing the storage volume
    of the variable bytes: 0-127 single-byte, double-byte storage 128-2047,> 2047 3-4byte
  • 16-UTF
    2 byte character storage (2byte as additional identification)
  • UTF-32
    4 byte
• Built-in functions
  • ord ( 'A')> 65 acquires the character code point
  • chr (104)> h acquires the character corresponding to the current code point
  • str.encode ( 'coding') a specific character encoding
  • bytes.decode ( 'coding') decoded as the character encoding text characters
  • sys.getdefaultencoding () to view the system default encoding format
• Type Conversion
  • bytes
    manual claiming B ''
    string code str.encode ()
    Constructor bytes (STR, 'coding') into encoded string (not exceed 256, by default only process one byte)
  • bytearray - list of similar properties may be employed
    ByteArray ( 'byte', 'coding')
    .decode () decodes a string
• BOM processing byte order mark
  open ( 'data.txt', 'r | w', encoding = 'utf-8-to’)