File operation ②

Binary

mode parameter in the open() method:

• Tread text file (default)
• b read binary

Binary operation by changing mode parameter

file_name = 'DD.jpg'

# Read mode
# Tread text file (default)
# b read binary

# t b and r w a are added together. They are all parameters of mode

with open(file_name,'rb') as file_obj :
	'''
	//Read the binary code of picture DD.jpg and write it to picture.jpg

	'''
	# When reading a text file, the size is in characters
	# When reading binary files, size is in bytes
	# print( file_obj.read(100) )

	new_name = 'picture.jpg' 

	with open( new_name ,'wb' ) as new_obj :

		chunk = 1024*100 # Size per read

		while True :
			content = file_obj.read(chunk) # Intermediate variable, storing the read information

			if not content :
				# Read empty, read completed
				break

			new_obj.write( content ) # Write in

File read location

• seek() and tell() methods adjust and view pointer position

# seek() and tell()
with open('demo.txt','rb') as file_obj :
	# print( file_obj.read(100) )
	# print( file_obj.read(20) )

	# The seek (offset [, when]) method can modify the position of the current read (pointer)
	# seek has two parameters:
	#     The first parameter offset is the backward offset relative to a position, which can be negative, and the position is determined by the second parameter
	#     The second parameter is the position calculation method
	#         When = 0 (default), from the beginning to the back;
	#         When = 1, backward from the current position;
	#         When = 2, relative to the move at the end of the file, offset usually takes a negative value

	file_obj.seek(10)
	print( 'Current pointer at:',file_obj.tell() )
	print( file_obj.read(3) )

	file_obj.seek(20,1)
	print( 'Current pointer at:',file_obj.tell() )
	print( file_obj.read(3) )

	file_obj.seek(-10,2)
	print( 'Current pointer at:',file_obj.tell() )
	print( file_obj.read(10) )

	# The call () method can be used to view the current read (pointer) position
	print( 'Current pointer at:',file_obj.tell() )

print('- '*20,'I'm a gorgeous dividing line',' -'*20)

# When reading Chinese
with open('demo2.txt','rt',encoding = 'utf-8') as file_obj :

	seek_size = 3
	file_obj.seek(seek_size) 
	# seek_size is in bytes, a complete Chinese is three bytes,
	# 	Therefore, in order to ensure the integrity of the text, it is necessary to report an error

	read_size = 2
	print( file_obj.read(read_size) ) 
	# Because the text file ('rt ', t is the text file) is read at this time,
	# 	So read_size is based on characters. A Chinese character is a character

	print( 'Current pointer at:',file_obj.tell() )
	# At this time, the pointer position is 9, 3 + 2 * 3 = 9

Other operations on files

• listdir() returns directory information
• getcwd() get directory information
• chdir() switch to directory
• mkdir() create directory
• remove() delete directory
• rename() renames and moves the path of a file

import os
from pprint import pprint
# Introducing pprint method from pprint module

# os.listdir( path = '.' ) 
# If a path is required as a parameter, the directory structure under the path will be obtained. The default value is the current directory,
# Returns a list of directory structures, each file (folder) is an element in the table
r = os.listdir( )
pprint( r )

# os.getcwd() gets the current directory
r = os.getcwd( )
print( r ) 

# Os.chdir (path) switches the current directory
# A path is required as a parameter, which will be switched to

os.chdir('..') # Go to the parent directory

r = os.getcwd( )
print( r ) 

# os.mkdir('path\name ') create directory (folder)
# If the parameter is a folder name directly, it will be created in the current directory
# It can also be path + folder name, which is created under the specified path
os.mkdir('aa') 
os.mkdir('06.Exceptions and documents/aa') 

# os.remove() delete directory
# Parameters are the same as above.
os.rmdir('aa') 
os.rmdir('06.Exceptions and documents/aa') 


os.chdir('06.Exceptions and documents')
# Go back to 06. Exception and file directory
open('a.txt','x' ) # Create a.txt file

# os.remove() delete file
# Parameters can be path + filename
os.remove('a.txt')


# os.rename('old name ',' new name ') can rename and move a file path
# Both parameters can be path + filename
# open('aa.txt','x' ) 
os.rename('aa.txt','bb.txt')