Python - Working Code Sample for OS and Sys Modules

Working Code Sample for OS and Sys Modules in Python

Python’s os and sys modules are part of the standard library and provide vital functionality for interacting with the operating system and the Python runtime environment. These modules empower developers to perform system-level operations, manipulate the environment, and handle runtime arguments. This document provides a thorough overview along with working examples for both modules in various use cases.

Introduction to OS and Sys Modules

Importing Required Modules

import os
import sys

These modules are available by default in Python, so no additional installation is required.

Working with OS Module

Getting Current Working Directory

cwd = os.getcwd()
print("Current Working Directory:", cwd)

Changing the Current Working Directory

os.chdir('/tmp')
print("New Working Directory:", os.getcwd())

Listing Files and Folders in Directory

items = os.listdir('.')
print("Directory Contents:", items)

Creating Single and Nested Directories

os.mkdir('example_dir')
os.makedirs('parent/child/grandchild')
print("Directories created.")

Removing Directories

os.rmdir('example_dir')
os.removedirs('parent/child/grandchild')

Renaming Files or Folders

os.rename('old.txt', 'new.txt')
print("File renamed.")

Deleting a File

os.remove('unwanted.txt')

Check if File or Directory Exists

print("Exists:", os.path.exists('file.txt'))
print("Is file:", os.path.isfile('file.txt'))
print("Is directory:", os.path.isdir('folder'))

Path Operations Using os.path

Joining Paths

path = os.path.join('folder', 'subfolder', 'file.txt')
print("Joined path:", path)

Splitting Path into Directory and File

full_path = '/home/user/data.csv'
print("Directory:", os.path.dirname(full_path))
print("Filename:", os.path.basename(full_path))

Getting Absolute Path

print("Absolute path:", os.path.abspath('script.py'))

Getting File Information

Get File Size

print("File size:", os.path.getsize('data.txt'), "bytes")

Last Modified and Access Time

import time

modified = os.path.getmtime('data.txt')
accessed = os.path.getatime('data.txt')

print("Modified:", time.ctime(modified))
print("Accessed:", time.ctime(accessed))

Accessing Environment Variables

List All Environment Variables

env = os.environ
print(env)

Access a Specific Environment Variable

home = os.environ.get('HOME')
print("Home Directory:", home)

Set and Modify Environment Variable

os.environ['MY_VAR'] = 'TestValue'
print("MY_VAR:", os.environ['MY_VAR'])

Process Management with OS

Get Current and Parent Process IDs

print("Current PID:", os.getpid())
print("Parent PID:", os.getppid())

Execute a Shell Command

os.system('echo Hello from shell')

Walking Through Directories

Using os.walk

for root, dirs, files in os.walk('.'):
    print("Directory:", root)
    print("Subdirectories:", dirs)
    print("Files:", files)

Common File Utilities

Cleanup Files with Extension

for filename in os.listdir('.'):
    if filename.endswith('.log'):
        os.remove(filename)
        print("Deleted:", filename)

Backup Files

import shutil

def backup(file):
    if os.path.exists(file):
        shutil.copy(file, file + '.bak')
        print("Backup created for", file)

backup('sample.txt')

Working with Sys Module

Get Command-Line Arguments

print("All arguments:", sys.argv)

if len(sys.argv) > 1:
    print("Script received argument:", sys.argv[1])

Exit from Python Program

print("Exiting now...")
sys.exit(0)

Python Version Information

print("Python version:", sys.version)
print("Version info:", sys.version_info)

System Path List

print("System path:", sys.path)

Adding Directory to Module Search Path

sys.path.append('/my/custom/modules')

Standard Input and Output

sys.stdout.write("Hello via stdout\n")
user_input = sys.stdin.readline()
print("You typed:", user_input)

Exception Hook Example

def custom_hook(exctype, value, traceback):
    print("An error occurred:", value)

sys.excepthook = custom_hook
raise ValueError("This will trigger custom hook")

Combining OS and Sys for Real Use Cases

Example 1: CLI File Checker

if len(sys.argv) != 2:
    print("Usage: python script.py <filename>")
    sys.exit(1)

filename = sys.argv[1]
if os.path.exists(filename):
    print("File exists.")
else:
    print("File does not exist.")

Example 2: Environment-Specific Behavior

mode = os.environ.get('APP_MODE', 'development')
print("Running in mode:", mode)

if mode == 'production':
    print("Running optimized processes...")
else:
    print("Running in debug mode...")

Example 3: Script Location and Resources

script_path = os.path.abspath(sys.argv[0])
script_dir = os.path.dirname(script_path)
resource_path = os.path.join(script_dir, 'data.json')
print("Script Directory:", script_dir)
print("Resource Path:", resource_path)

Handling Errors

File Not Found

try:
    os.remove('missing.txt')
except FileNotFoundError:
    print("File not found.")

Permission Error

try:
    os.remove('/etc/important')
except PermissionError:
    print("Permission denied.")

Invalid Arguments

if len(sys.argv) != 3:
    print("Usage: python script.py input.txt output.txt")
    sys.exit(1)

Advanced Tips

Set Default Encoding

print("Encoding:", sys.getdefaultencoding())

Redirect Output to a File

with open('output.txt', 'w') as f:
    sys.stdout = f
    print("This will go to output.txt")
    sys.stdout = sys.__stdout__

Check Platform

print("Platform:", sys.platform)
if sys.platform == "win32":
    print("Running on Windows")
elif sys.platform == "linux":
    print("Running on Linux")

Summary of os and sys Functions

• os.getcwd(), os.chdir() - Directory management
• os.mkdir(), os.makedirs() - Directory creation
• os.remove(), os.rename() - File management
• os.environ, os.system() - Environment and shell
• os.path - Path operations
• sys.argv, sys.exit() - CLI and exit
• sys.version, sys.path - Runtime info

In this guide, we explored Python’s os and sys modules through practical, working examples. These modules are essential for creating flexible, OS-aware scripts that can handle real-world tasks such as file manipulation, directory traversal, environment configuration, and command-line utilities.

The os module interacts directly with the file system and environment variables, while the sys module handles the runtime state and CLI arguments. When used together, they can automate and control everything from startup behavior to deployment utilities.

Whether you're building administrative tools, scripting system tasks, or creating development frameworks, mastery over these modules will dramatically improve your productivity and control in Python.