Python 3 - os.lseek() Method

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Description

The method lseek() sets the current position of file descriptor fd to the given position pos, modified by how.

Syntax

Following is the syntax for lseek() method −

os.lseek(fd, pos, how)

Parameters

• fd − This is the file descriptor, which needs to be processed.

• pos − This is the position in the file with respect to given parameter how. You give os.SEEK_SET or 0 to set the position relative to the beginning of the file, os.SEEK_CUR or 1 to set it relative to the current position; os.SEEK_END or 2 to set it relative to the end of the file.

• how − This is the reference point with-in the file. os.SEEK_SET or 0 means beginning of the file, os.SEEK_CUR or 1 means the current position and os.SEEK_END or 2 means end of the file.

Defined pos constants

• os.SEEK_SET - 0
• os.SEEK_CUR - 1
• os.SEEK_END - 2

Return Value

This method does not return any value.

Example

The following example shows the usage of lseek() method.

#!/usr/bin/python3
import os, sys

# Open a file
fd = os.open( "foo.txt", os.O_RDWR|os.O_CREAT )

# Write one string
line = "This is test"
b = line.encode()
os.write(fd, b)

# Now you can use fsync() method.
# Infact here you would not be able to see its effect.
os.fsync(fd)

# Now read this file from the beginning
os.lseek(fd, 0, 0)
line = os.read(fd, 100)
print ("Read String is : ", line.decode())

# Close opened file
os.close( fd )

print ("Closed the file successfully!!")

Result

When we run the above program, it produces the following result −

Read String is :  This is test
Closed the file successfully!!