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System and OS Modules (os, sys, subprocess, shutil)

Python provides standard library modules to interact directly with the operating system, execute system commands, manage files, and control program execution.

1. The os Module

The os module provides functions for interacting with the operating system.

Common File and Directory Operations

Function Description
os.getcwd() Returns the current working directory as a string
os.chdir(path) Changes current working directory
os.listdir(path) Returns a list of all entries in the directory
os.mkdir(path) Creates a single new directory
os.makedirs(path) Creates a directory and any missing parent directories
os.remove(path) Deletes a file
os.rmdir(path) Deletes an empty directory
Example: Working Directory and Environment Variables
import os

# Current working directory
cwd = os.getcwd()
print("Current Directory:", cwd)

# Accessing environment variables
user_home = os.environ.get("HOME") or os.environ.get("USERPROFILE")
print("User Home:", user_home)

2. The sys Module

The sys module provides variables and functions that interact directly with the Python interpreter.

Important Attributes and Functions

Property / Method Description
sys.argv List of command-line arguments passed to the script
sys.exit(code) Exits the Python interpreter (default code 0 means success)
sys.path List of directory strings where Python looks for modules
sys.version Python interpreter version string
sys.platform Operating system platform identifier (win32, darwin, linux)
Example: Inspecting sys Information
import sys

print("Python Version:", sys.version.split()[0])
print("Platform:", sys.platform)
print("Script Name:", sys.argv[0])
Output
Python Version: 3.14.7 Platform: win32 Script Name: script.py

3. The shutil Module

While os works with individual files and directories, shutil provides high-level operations on files and collections of files.

Example: Copying and Moving Files
import shutil

# Copy a single file
# shutil.copy("source.txt", "backup.txt")

# Copy an entire directory tree recursively
# shutil.copytree("src_folder", "backup_folder")

# Delete a directory and all of its contents
# shutil.rmtree("temp_folder")

4. The subprocess Module

The subprocess module is the standard way to start new processes, run external commands, and capture their input/output.

Syntax of subprocess.run()

subprocess.run(args, capture_output=False, text=False, check=False)
Example: Executing a Shell Command
import subprocess

# Run command and capture output as text
result = subprocess.run(["python", "--version"], capture_output=True, text=True, check=True)

print("Return Code:", result.returncode)
print("Standard Output:", result.stdout.strip())
Output
Return Code: 0 Standard Output: Python 3.14.7