python file operation summary

Posted by Toggles on Wed, 15 May 2019 07:47:56 +0200

File operation of python

Opening and Closing of Files

open (File Name, Access Mode) - open Files

demo: 
file = open('test.txt', 'w')

close() - Close the file

demo:
file = open('test.txt', 'w')

file.close()

Access pattern description

r: Open the file read-only. The pointer to the file will be placed at the beginning of the file, which is the default mode.
w: Open a file for writing only, overwrite it if it already exists, and create a new file if it does not exist.
A: Open a file for appending. If the file already exists, the file pointer will be placed at the end of the file. That is to say, the new content will be written to the existing content, if the file does not exist, create a new file for writing.
rb: Open a file in binary format for read-only. The file pointer will be placed at the beginning of the file, which is the default mode.
wb: Opening a file in binary format is only for writing. If the file does not exist, create a new file.
ab: Open a file in binary format for appending. If the file already exists, the file pointer will be placed at the end of the file, that is, the new content will be written after the existing content. If the file does not exist, create a new file for writing.
r+: Open a file for reading and writing, and the file pointer will be placed at the beginning of the file.
w+: Open a file for users to read and write, and overwrite it if it already exists. If the file does not exist, create a new file.
A+: Open a file for users to read and write. If the file already exists, the file pointer will be placed at the end of the file. When a file is opened, it will be appended. If the file does not exist, create a new file for users to read and write.
rb+: Open a file in binary format for reading and writing. The file pointer will be placed at the beginning of the file.
wb +: Open a file in binary format for reading and writing, and overwrite it if it already exists. If the file does not exist, create a new file.
ab+: Open a file user append in binary format, and if the file already exists, the file pointer will be placed at the end of the file.

write Write Data

Writing data to a file can be accomplished using write()

demo: 
file = open('test.txt', 'w')
file.write('hello world')
file.close()

Note: If the file does not exist, create the file. If the file exists, it is emptied first and then written to the data.

read Read read Data

Data can be read from a file using read(num), which represents the length of the data to be served from the file (in bytes), and if no num is passed in, it means reading all the data in the file.

demo: 
f = open('test.txt', 'r')
#Up to 5 data reads
content = f.read(5) 
print(content)

print("-"*30)
#Continue reading all the remaining data from the last read position
content = f.read()
print(content)
#Note: Close file is required
f.close()
#Result:
hello
-----------------------------
world

Note: If you open a file with open, if you use "r", you can omit it, that is, write only open('test.txt').

readlines Read Data

readlines, like read without parameters, reads the contents of the entire file in a row-by-row fashion, and returns a list in which the data of each row is an element.

demo: 
f = open('test.txt', 'r')
content = f.readlines()
print(type(content))

i = 1
for temp in content:
	print("%d:%s" % (i, temp))
	i += 1
f.close()

readline Read Data

demo: 
f = open('test')

content = f.readline()
print("1:%s" % content)

content = f.readline()
print("2:%s" % content)

f.close()
//Result:
1:hello world
2:hello world

Make backups of files

Enter the name of the file, and the program automatically backs up the file.

demo: 
#Prompt for file name
oldFileName = input("Please enter the name of the file to be copied:")

#Open files in a read-only manner
oldFile = open(oldFileName, 'rb')

#Extract the suffix of the file
fileFlagNum = oldFileName.rfind('.')
fileFlagNum = 4
#rfind() returns the location of the last occurrence of the string, and - 1 if there is no match
#rfind() method syntax: str.rfind(str, start=0 end=len(string))

if fileFlagNum > 0:
	#Using subscripts to obtain values [4:]
	fileFlag = oldFileName[fileFlagNum:]

#Organize new file names
newFileName = oldFileName[:fileFlagNum] + 'Duplicate' + fileFlag

#Organizing new documents
newFile = open(newFileName, 'wb')

#Copy data from old files, line by line, to new files
for lineContent in oldFile.readlines():
	newFile.write(lineContent)
#Close File
oldFile.close()
newFile.close()

Document-related operations

os.rename() rename

Rename (filename to be modified, new filename)

demo: 
import os
os.rename('1.txt', '2.txt')

Os. remove (file name to be deleted)

demo: 
import os
os.remove('2.txt')

os.getcwd() Gets the current directory

demo:
import os
os.getcwd()

os.chdir() Change the default directory

demo:
import os
os.chdir("../")

os.listdir() Gets a list of directories

demo:
import os
os.listdir("./")

os.rmdir() Delete folders

import os
os.rmdir("demo")

Batch modification of file names

demo: 
#Batch prefix file name
#Batch prefix file name
import os

funFlag = 1 #1 means add flag 2 means delete flag
folderName = './renameDir/'

#Gets all file names for the specified path
dirList = os.listdir(folderName)

#Traverse to output all file names
for name in dirList:
print(name)

if funFlag == 1:
    newName = '[Shi Ge produce]-' + name
elif funFlag == 2:
    num = len('[Shi Ge produce]-')
    newName = name[num:]
print newName

os.rename(folderName+name, folderName+newName)

Topics: Python

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