⚡ IT Wisdom How many DevOps engineers does it take to change a lightbulb? All of them. One to change it, the rest to argue about whether to containerize it first.
Skilled Practitioner
4249 XP 1751 to Expert
Learn  /  Python Fundamentals  /  Unit 12

Unit 12 — Virtual Environments and Packages — Isolating Your Dependencies

Units
✓ Whetting Your Appetite — Why Python for Networking? ✓ Using the Python Interpreter ✓ An Informal Introduction to Python — Network Basics ✓ Control Flow — Making Decisions in Network Scripts ✓ Data Structures — Modeling Network Inventories ✓ Modules — Organizing Your Network Scripts ✓ Input and Output — Reading and Writing Network Data ✓ Errors and Exceptions — Building Reliable Network Scripts ✓ Classes — Modeling Network Devices as Objects ✓ Standard Library Part I — Tools Every Network Script Needs ✓ Standard Library Part II — Logging, Formatting, and Counting ✓ Virtual Environments and Packages — Isolating Your Dependencies ✓ Capstone — Build a Network Inventory Tool

Why Virtual Environments?

When you install a package with pip install requests, it goes into your system Python. If two projects need different versions of the same package, they conflict. A virtual environment is an isolated Python installation for one project — it has its own packages, its own pip, and leaves your system Python untouched.

Every real Python project uses one. In network automation, this matters: netmiko 4.x and 3.x have breaking API changes. Without a venv, updating one project breaks another.

Creating and Activating a venv

python3 -m venv venv

This creates a venv/ directory in your project folder. Activate it:

source venv/bin/activate        # Linux / macOS
venv\Scripts\activate           # Windows

Your prompt changes to show (venv) — any python3 or pip command now uses the isolated environment.

Deactivate when done:

deactivate

Installing Packages

With the venv active, install packages normally:

pip install requests
pip install requests==2.31.0    # pin a specific version
pip install "requests>=2.28"    # minimum version constraint

List installed packages:

pip list

Show details about one package:

pip show requests

requirements.txt — Sharing Your Dependencies

requirements.txt lists all the packages your project needs so others (or the Pi) can install the same set with one command.

Freeze your current environment to generate the file:

pip freeze > requirements.txt

This writes every installed package and its exact version, for example:

certifi==2024.2.2
charset-normalizer==3.3.2
idna==3.6
requests==2.31.0
urllib3==2.2.1

Install from a requirements file on another machine or after cloning:

pip install -r requirements.txt

What Goes in .gitignore

The venv/ directory contains thousands of files — never commit it. Add it to .gitignore:

venv/
__pycache__/
*.pyc
.env

Commit requirements.txt instead. Anyone who clones the repo runs pip install -r requirements.txt to recreate the environment.

Checking Which Python You Are Using

which python3          # /home/emmy/myproject/venv/bin/python3
python3 --version      # Python 3.11.x
pip --version          # pip 24.x from .../venv/lib/...

If the path shows venv/bin/, the venv is active. If it shows /usr/bin/, you are in the system Python.

Summary

  • python3 -m venv venv creates an isolated environment in venv/
  • source venv/bin/activate activates it — your prompt shows (venv)
  • pip install <package> installs only into the active venv
  • pip freeze > requirements.txt captures all installed versions
  • pip install -r requirements.txt recreates the environment elsewhere
  • Never commit venv/ — commit requirements.txt instead