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Python | os.lseek() method

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  • Last Updated : 22 Nov, 2019

OS module in Python provides functions for interacting with the operating system. OS comes under Python’s standard utility modules. This module provides a portable way of using operating system dependent functionality.

os.lseek() method sets the current position of file descriptor fd to the given position pos which is modified by how.

Syntax: os.lseek(fd, pos, how)

Parameters: 
fd:  This is the file descriptor on which seek is to be performed.
pos:  This is the position in the file with respect to given parameter how.
It can accept three values which are 
  • os.SEEK_SET or 0 to set the position relative to the beginning of the file
  • os.SEEK_CUR or 1 to set the position relative to the current position
  • os.SEEK_END or 2 to set the position relative to the end of the file.
how: This is the reference point in the file. It also accepts three values which are
  • os.SEEK_SET or 0 to set the reference point to the beginning of the file
  • os.SEEK_CUR or 1 to set the reference point to the current position
  • os.SEEK_END or 2 to set the reference point to the end of the file.
Return Value: This method does not returns any value. Example #1 : Using os.lseek() method to seek the file from beginning
# Python program to explain os.lseek() method 
        
# importing os module 
import os 
    
# path 
path = 'C:/Users/Rajnish/Desktop/testfile.txt'
  
# Open the file and get
# the file descriptor associated
# with it using os.open() method
fd = os.open(path, os.O_RDWR|os.O_CREAT)
  
# String to be written
s = 'GeeksforGeeks - A Computer Science portal'
  
# Convert the string to bytes 
line = str.encode(s)
  
# Write the bytestring to the file 
# associated with the file 
# descriptor fd 
os.write(fd, line)
  
# Seek the file from beginning
# using os.lseek() method
os.lseek(fd, 0, 0)
  
# Read the file
s = os.read(fd, 13)
  
# Print string
print(s)
  
# Close the file descriptor 
os.close(fd)
Output:
b'GeeksforGeeks'

Example #2 :

Using os.lseek() method to to seek the file from specific position




# Python program to explain os.lseek() method 
        
# importing os module 
import os 
    
# path 
path =  'C:/Users/Rajnish/Desktop/testfile.txt'
  
# Open the file and get
# the file descriptor associated
# with it using os.open() method
fd = os.open(path, os.O_RDWR|os.O_CREAT)
  
# String to be written
s = 'GeeksforGeeks'
  
# Convert the string to bytes 
line = str.encode(s)
  
# Write the bytestring to the file 
# associated with the file 
# descriptor fd 
os.write(fd, line)
  
  
# Seek the file after position '2'
# using os.lseek() method
os.lseek(fd, 2, 0)
  
# Read the file
s = os.read(fd, 11)
  
# Print string
print(s)
  
# Close the file descriptor 
os.close(fd)
Output:
b'eksforGeeks'

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