Python Virtual Environments

Why Virtual Environments?

If you install all packages globally, two projects needing different versions of the same library will conflict. A virtual environment is an isolated Python installation per project — each project gets its own packages and versions, completely independent of others. Always use one for every Python project; it's the professional standard.

Create and Activate

Python's built-in venv module creates the environment. After activating, your terminal prompt shows the environment name and all pip installs go into that isolated folder.

# Create
python -m venv myenv

# Activate on Mac/Linux
source myenv/bin/activate

# Activate on Windows
myenv\Scripts\activate

# Prompt now shows:
(myenv) $

(myenv) $

Install Packages and Save Dependencies

# Install into the virtual environment
pip install requests flask pandas

# Save exact versions
pip freeze > requirements.txt

# Deactivate when done
deactivate

Successfully installed flask-3.0.0 pandas-2.1.4 requests-2.31.0

Recreating from requirements.txt

Never commit the venv/ folder — it's large and platform-specific. Commit requirements.txt instead. Anyone can recreate the exact environment with one command.

# After cloning a repo:
python -m venv myenv
source myenv/bin/activate
pip install -r requirements.txt

Successfully installed all packages.