Day10 Python Study Notes & Key Points of Attention

Part 1: Python study notes

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12. object persistence

12.1. Flat file

12.1.1. Text File

Text files are stored persistent objects
Convert the string you pass over to Python expressions, so that you can run the same statement when Python
Examples

 1 #文本文件存储持久化对象
 2 
 3 scores = [88,99,77,55]
 4 
 5 def write_scores():
 6     with open('data_list.txt','w',encoding='utf8') as f:
 7         f.write(str(scores))
 8         print('File writing completed......')
 9 
10 def read_scores():
11     with open('data_list.txt','r' , Encoding = ' UTF8 ' ) AS F:
 12 is          LST = the eval (reached, f.read ())     # your pass over the string into a Python expression, so that you can run the same statement as Python 
13 is  
14          LST [0] 99 =
 15          Print (LST)
 16  
. 17  IF  the __name__ == ' __main__ ' :
 18 is      # write_scores () # First RUN to the this data_list.txt The Create File 
. 19      read_scores ()

12.2.pickle

12.2.1.pickle module

Serialized bit string
- .dumps (obj): the target sequence into a string
- .loads (s): The hair string conversion target sequence
- Examples

1 import pickle
2 person = {'name':'Tom','age':20}
3 s = pickle.dumps(person)
4 s

Run Results: b '\ x80 \ x03} q \ x00 (X \ x04 \ x00 \ x00 \ x00nameq \ x01X \ x03 \ x00 \ x00 \ x00Tomq \ x02X \ x03 \ x00 \ x00 \ x00ageq \ x03K \ x14u.'

1 p = pickle.loads(s)
2 p

Run Results: { 'name': 'Tom', 'age': 20}

Serialized object to a file
- .dump(obj,file)
- .load(file)
- Examples

1 person = {'name':'Tom','age':20}
2 pickle.dump(person,open('pickle.db','wb'))
3 p = pickle.load(open('pickle.db','rb'))
4 p

Run Results: Out [14]: { 'name': 'Tom', 'age': 20}

12.3.shelve

12.3.1.shelve

The existence of multiple objects in a document

.open('dbfile')
.close()
db['key'] = obj
len (db)
del db['key']
Examples

. 1  # Shelve serialized custom class Example 
2  
. 3  Import The shelve
 . 4  
. 5  class Student:
 . 6      DEF  the __init__ (Self, name, Age):
 . 7          the self.name = name
 . 8          self.age = Age
 . 9  
10  
. 11      DEF  __str__ (Self):
 12 is          return the self.name
 13 is  
14  DEF write_shelve ():
 15          S = Student ( ' Tom ' , 20 is )
 16          DB = shelve.open ( 'shelve_student_db')
17         db['s'] = s
18         db.close()
19 
20 def read_shelve():
21     db = shelve.open('shelve_student_db')
22     st = db['s']
23     print(st)
24     print(st.name)
25     print(st.age)
26     db.close()
27 
28 
29 if __name__ == '__main__':
30     # write_shelve()    # First run this so that the shelve_student_db.* files can be created
31     read_shelve()

12.4. Database

12.5.ORM

13. String

13.1. Overview

13.1.1 Type

str string
bytes bytes
byte array bytearray

13.1.2. 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
Character encoding architecture diagram:

13.1.3. Strings are stored

Encoding only acts on the file storage media or intermediate conversion
Always stored in memory after the decoded text

13.2. Character Encoding

13.2.1.ASCII

Stored in a Byte 0-127
Stored in a Byte 128-255
Variable byte

13.2.2.latin-1

13.2.3.UTF-8

• 0-127 single-byte

• 128-2047 double-byte storage

• > 2047 3-4 Byte

• Use 128-255 per Byte

13.2.4.UTF-16

2 Byte store character (as identified plus 2 Byte)
4 Byte

13.2.5.UTF-32

13.3. Built-in functions

13.3.1.ord () Gets the character code point

13.3.2.chr () Gets a character code corresponding to the point

13.3.3.str.encode ( 'coding') a specific character encoding

13.3.4.bytes.decode ( 'coding') character encoding and decoding text characters

13.3.5.encode and decode example

. 1 S1 = ' ABCD ' 
2 s1.encode ( ' the ASCII ' )
 . 3  
. 4 S2 = ' Youpin class ' 
. 5 s2.encode ( ' UTF-. 8 ' )
 . 6  
. 7 B1 = B ' \ XE4 \ XBC \ X98 \ xe5 \ X93 \ X81 \ xe8 \ XAF \ XBE \ xe5 \ XA0 \ X82 ' 
. 8  
. 9 b1.decode ( ' UTF-. 8 ' ) -> ' excellent product class ' 
10 b1.decode ( ' UTF-16 ' ) -> see garbled

Note: encode and decode, the default encoding is utf-8

1 import sys
2 sys.getdefaultencoding()
3 
4 --> utf-8

13.3.6. Formulate example when encoding type document processing

1 open('data.txt','w',encoding='utf-8').write('优品课堂')
2 open('data.txt','r',encoding='utf-8').read()