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Python | os.open() method - GeeksforGeeks

Python | os.open() method

Last Updated : 11 Jul, 2025

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.open() method in Python opens a specified file path. This method returns a file descriptor for a newly opened file. The returned file descriptor is non-inheritable.

os.open method is also used to set various flags according to the specified flags and file's mode according to the specified mode.

Syntax:

os.open(path, flags, mode = 0o777, *, dir_fd = None)

Parameters:

Path: A path-like object representing the file system path. This is the file path to be opened. A path-like object is a string or bytes object which represents a path.
flags: This parameter specifies the flags to be set for newly opened files.
mode (optional): A numeric value representing the mode of the newly opened file. The default value of this parameter is 0o777 (octal).
dir_fd (optional): A file descriptor referring to a directory.

Return Type:

This method returns a file descriptor for a newly opened file.

List of flags that you can set on the new file:

List of Flags

Flag Description os.O_RDONLY Opens the file in read-only mode. os.O_WRONLY Opens the file in write-only mode. os.O_RDWR Opens the file in read and write mode. os.O_NONBLOCK Opens the file in non-blocking mode. os.O_APPEND Opens the file and places the cursor at the end of the contents. os.O_CREAT Creates a file if it doesn’t exist. os.O_TRUNC Truncates a file size to 0. os.O_EXCL Shows an error while creating a file that already exists. os.O_SHLOCK Obtains a shared lock for a file atomically. os.O_EXLOCK Obtains an exclusive lock for a file atomically. os.O_DIRECT Removes or reduces cache effects in a file. os.O_FSYNC Writes file synchronously. os.O_NOFOLLOW Sets the file that doesn’t follow a symlink. How to use the os.open() method

We will use the os.open() method to open a file path. Look at the code below to understand it better:

Code:

Python3


 # importing os module 
import os
# File path to be opened
path = './file9.txt'
# Mode to be set 
mode = 0o666
# flags
flags = os.O_RDWR | os.O_CREAT
fd = os.open(path, flags, mode)
print("File path opened successfully.")
str = "GeeksforGeeks: A computer science portal for geeks."
os.write(fd, str.encode())
print("String written to the file descriptor.") 
# Now read the file from beginning
os.lseek(fd, 0, 0)
str = os.read(fd, os.path.getsize(path))
print("\nString read from the file descriptor:")
print(str.decode())
# Close the file descriptor
os.close(fd)
print("\nFile descriptor closed successfully.")

Output

File path opened successfully.
String written to the file descriptor.

String read from file descriptor:
GeeksforGeeks: A computer science portal for geeks.

File descriptor closed successfully.

In this tutorial, we have covered the os.open() method of the OS module to open a file. It is a very easy and straightforward way of opening files in Python.

We have explained how to use os.open() method with a sample Python program. This easy and simple tutorial will help you implement the os.open() method in your codes.

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