Python Packaging

Also Known As

TL;DR

Explanation

Modern Python packaging: pyproject.toml (PEP 517/518) replaces setup.py and setup.cfg. Poetry: pyproject.toml + poetry.lock, integrated virtual env management, publish to PyPI. PDM: PEP 582, fast resolver. Key commands: poetry add (install + update lock), poetry install (from lock file, deterministic), poetry install --only main (production — no dev deps). Lock files ensure reproducible installs across environments. Virtual environments isolate project dependencies. PHP analogy: Poetry is to Python as Composer is to PHP.

Common Misconception

Why It Matters

Common Mistakes

• No lock file committed to git — non-deterministic installs across environments
• pip install in production instead of poetry install --only main — installs dev tools
• Not using virtual environments — global installs conflict between projects
• Mixing pip and poetry in the same project — breaks lock file integrity

Code Examples

# requirements.txt — no locking, no separation:
requests
flask
pytest    # Dev tool in production!
black     # Dev tool in production!
# Different versions installed on different days

# pyproject.toml with Poetry:
[tool.poetry.dependencies]
python = '^3.11'
requests = '^2.31'
flask    = '^3.0'

[tool.poetry.group.dev.dependencies]
pytest = '^7.4'
black  = '^23.0'

# Commands:
# poetry install            # From lock file — deterministic
# poetry install --only main # Production: no dev deps
# poetry add requests       # Adds + updates poetry.lock
# git add pyproject.toml poetry.lock

References

• ↗ https://python-poetry.org/docs/

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