Cheat SheetsPython A–ZPackaging & venv

Packaging & venv — Cheat Sheet

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Cheat Sheet · AiCanCode.org
Packaging & venv
Python A–Z2 topicsQuick revision reference
1

Virtual Environments & pip — Isolating Every Project

python -m venv .venv gives each project its own interpreter and packages; pip installs into it; requirements.txt with pinned versions makes the setup reproducible on any machine.

  • ✓One venv per project; global installs are how projects break each other
  • ✓Activate first — then python/pip mean the project-local copies
  • ✓pip freeze > requirements.txt pins exact versions; commit the file, ignore .venv/
  • ✓Same requirements.txt drives teammates, CI, and Docker builds; uv is the fast modern drop-in
create → activate → install → work → deactivate
# Create (once per project, inside the project folder)
python -m venv .venv

# Activate (every new terminal session)
.venv\Scripts\activate           # Windows
source .venv/bin/activate         # macOS / Linux
# prompt becomes:  (.venv) C:\projects\campus-api>

# Install packages — they go into .venv only
pip install requests "fastapi[standard]" sqlalchemy

pip list                          # what is installed here
pip show requests                 # version, dependencies, location

# Leave the environment
deactivate

# .gitignore MUST contain:
# .venv/
2

Packaging with pyproject.toml — From Script to Installable Package

pyproject.toml is the single modern config for a Python package: metadata, dependencies, and console scripts in one file — pip install -e . for development, python -m build + twine to publish.

  • ✓pyproject.toml is the modern standard — setup.py is legacy
  • ✓src/ layout prevents "works locally, breaks installed" import bugs
  • ✓pip install -e . = editable mode: edits apply without reinstalling
  • ✓[project.scripts] creates console commands; build + twine publish to PyPI
One file replaces setup.py, setup.cfg and MANIFEST.in
# Project layout (src/ layout — the recommended one)
# campus-utils/
# ├── pyproject.toml
# ├── README.md
# └── src/
#     └── campus_utils/
#         ├── __init__.py
#         ├── cli.py
#         └── marks.py

# ── pyproject.toml ──────────────────────────────
[project]
name = "campus-utils"
version = "0.1.0"
description = "Marksheet and placement helpers"
requires-python = ">=3.10"
dependencies = [
    "requests>=2.31",
    "pydantic>=2.0",
]

[project.optional-dependencies]
dev = ["pytest", "ruff"]

[project.scripts]
campus = "campus_utils.cli:main"       # installs a real 'campus' command

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"
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