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Python | os.write() method

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  • Difficulty Level : Medium
  • Last Updated : 18 Jun, 2019
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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.write() method in Python is used to write a bytestring to the given file descriptor.

A file descriptor is small integer value that corresponds to a file that has been opened by the current process. It is used to perform various lower level I/O operations like read, write, send etc.

Note: os.write() method is intended for low-level operation and should be applied to a file descriptor as returned by or os.pipe() method.

Syntax: os.write(fd, str)

fd: The file descriptor representing the target file.
str: A bytes-like object to be written in the file.

Return Type: This method returns an integer value which represents the number of bytes actually written.

Code: Use of os.write() method to write a bytestring to a given file descriptor

# Python program to explain os.write() method 
# importing os module 
import os
# File path 
path = "/home / ihritik / Documents / GeeksForGeeks.txt"
# Open the file and get
# the file descriptor associated
# with it using method
fd =, os.O_RDWR)
# String to be written
s = "GeeksForGeeks: A Computer science portal for Geeks."
# Convert the string to bytes
line = str.encode(s)
# Write the bytestring to the file
# associated with the file
# descriptor fd and get the number of
# Bytes actually written
numBytes = os.write(fd, line)
print("Number of bytes written:", numBytes)
# close the file descriptor


Number of bytes written: 51
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