os Module Overview¶

The os module provides a portable way to interact with the operating system, including file operations, environment variables, and process management.

Mental Model

The os module is Python's bridge to the operating system. It wraps platform-specific system calls behind a single, portable API so your code works on Linux, macOS, and Windows without #ifdef gymnastics. Think of it as three toolkits in one: filesystem operations, environment variable access, and process management.

os Module Basics¶

Access operating system functionality.

```python import os

Get current working directory¶

cwd = os.getcwd() print(f"Current directory: {cwd}")

Get environment variables¶

path = os.environ.get('PATH', 'Not set') print(f"PATH exists: {bool(path)}")

Get OS name¶

print(f"OS: {os.name}")

Get system¶

import platform print(f"System: {platform.system()}") ```

Current directory: /home/user PATH exists: True OS: posix System: Linux

File and Directory Information¶

Get information about files and directories.

```python import os import tempfile

Create temp file for demo¶

with tempfile.NamedTemporaryFile(delete=False) as f: temp_path = f.name f.write(b"test content")

try: # Check file existence print(f"File exists: {os.path.exists(temp_path)}")

# Check file type
print(f"Is file: {os.path.isfile(temp_path)}")
print(f"Is dir: {os.path.isdir(temp_path)}")

# Get file size
print(f"Size: {os.path.getsize(temp_path)} bytes")

finally: os.unlink(temp_path) ```

File exists: True Is file: True Is dir: False Size: 12 bytes

Exercises¶

Exercise 1. Write a function file_info that takes a file path and returns a dictionary with "exists", "size", "is_file", and "is_dir" keys. Use os.path functions. Return size as 0 if the file does not exist.

Solution to Exercise 1

```python import os

def file_info(path): exists = os.path.exists(path) return { "exists": exists, "size": os.path.getsize(path) if exists else 0, "is_file": os.path.isfile(path), "is_dir": os.path.isdir(path), }

Test¶

print(file_info("/tmp"))

{'exists': True, 'size': ..., 'is_file': False, 'is_dir': True}¶

```

Exercise 2. Write a function current_directory_contents that returns a dictionary with two keys: "files" (list of file names) and "dirs" (list of directory names) in the current working directory. Use os.listdir and os.path.isfile/os.path.isdir.

Solution to Exercise 2

```python import os

def current_directory_contents(): cwd = os.getcwd() entries = os.listdir(cwd) return { "files": [e for e in entries if os.path.isfile(os.path.join(cwd, e))], "dirs": [e for e in entries if os.path.isdir(os.path.join(cwd, e))], }

Test¶

contents = current_directory_contents() print(f"Files: {len(contents['files'])}, Dirs: {len(contents['dirs'])}") ```

Exercise 3. Write a function get_os_info that returns a dictionary containing the current working directory, the OS name (os.name), and the path separator (os.sep).

Solution to Exercise 3

```python import os

def get_os_info(): return { "cwd": os.getcwd(), "os_name": os.name, "path_separator": os.sep, }

Test¶

info = get_os_info() for key, value in info.items(): print(f"{key}: {value}") ```