Venv

Python · Reference cheat sheet

📋 Overview

venv creates isolated Python environments so project dependencies do not clash with system packages. Always use a virtualenv per project; activate it before installing with pip.

🔧 Core concepts

Prefer python -m pip so you install into the active interpreter. .venv is the common directory name (gitignored).

💡 Examples

Create and use (PowerShell):

python -m venv .venv
.\.venv\Scripts\Activate.ps1
python -m pip install --upgrade pip
python -m pip install requests pytest

Create and use (bash):

python3 -m venv .venv
source .venv/bin/activate
python -m pip install -U pip
python -m pip install -r requirements.txt

Check which Python:

python -c "import sys; print(sys.executable)"
where python   # Windows
which python   # Unix

requirements pinning:

# requirements.txt
requests==2.32.3
pytest>=8.0,<9

⚠️ Pitfalls

• Installing with a global pip while thinking the venv is active — verify sys.executable.
• Committing .venv to git bloats the repo — ignore it.
• Mixing conda and venv accidentally — pick one workflow.
• Nested venvs and path confusion after IDE interpreter switches.
• On Windows, execution policy may block Activate.ps1 — adjust policy or use cmd activate.

🔗 Related

• Pip
• Packaging
• Import / export
• Testing with pytest
• Examples: cli tool
• Argparse