202 — Working with the OS and Environment Variables

Intermediate

Use Python's stdlib `os` module to read and write environment variables, inspect the running OS, and build portable file paths — then extend `deploy_check.py` to read DEPLOY_ENV, APP_VERSION, and a configurable base path from the environment so behaviour changes without touching argparse.

Learning Objectives

Read environment variables safely with os.getenv() and os.environ.get(), supplying defaults

Write and delete environment variables at runtime with os.environ

Inspect the running OS with os.uname(), os.getpid(), os.getcwd(), and os.cpu_count()

Build portable file paths with os.path.join(), os.path.expanduser(), os.path.dirname(), and os.path.basename()

Check path existence and metadata with os.path.exists(), os.path.isfile(), os.path.isdir(), and os.path.getsize()

Apply the environment-variable config pattern to make a script behaviour-configurable without argparse changes

Extend deploy_check.py to read DEPLOY_ENV, APP_VERSION, and BASE_DIR from the environment

Step 1

Set up the lesson 202 workspace

Create a dedicated directory, activate the virtual environment, and confirm the `os` module is available. `os` is part of the Python standard library — no pip install needed.

Commands to Run

mkdir -p ~/devops-python/lesson-202

cd ~/devops-python/lesson-202

source ~/devops-python/lesson-101/devops-env/bin/activate

python3 -c "import os; print('os module OK'); print('platform:', os.name)"

What This Does

The os module provides a portable interface to operating-system functionality: environment variables, process information, file-system path manipulation, and more. os.name returns 'posix' on Linux and macOS, 'nt' on Windows.

Because it is part of the standard library, import os is all you need — no installation step.

Expected Outcome

Your terminal prompt shows (devops-env).

The one-liner prints os module OK followed by platform: posix (on Linux or macOS).

Pro Tips

1
If you placed your virtual environment at a different path in Lesson 101, adjust the `source` command to match your actual venv location.
2
`os.name` is a coarse platform check. For finer-grained detection (distinguishing Linux from macOS), use `import platform; platform.system()` which returns `'Linux'`, `'Darwin'`, or `'Windows'`.

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