Compile pinned requirements from loose top-level dependencies with pip-compile (pip-tools) and keep a virtualenv exactly in sync with pip-sync
domain: python-dependency-management · 9 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Install pip-tools: pip install pip-tools
Create a requirements.in file listing only your top-level dependencies (e.g. django, requests). Valid sources for pip-compile are requirements.in, pyproject.toml, setup.cfg, or setup.py.
Run pip-compile requirements.in to generate a fully resolved requirements.txt with every transitive dependency pinned with == specifiers.
To upgrade a single package while keeping every other pin, run pip-compile -P <package> (--upgrade-package). Only that package is re-resolved; existing pins are preserved.
Commit BOTH requirements.in (source of truth) and requirements.txt (lock output) to version control.
In the target virtualenv, run pip-sync requirements.txt to make the environment exactly match the file: it installs missing packages, upgrades/downgrades mismatched ones, and uninstalls anything not listed.
With multiple files, run pip-sync requirements.txt dev-requirements.txt — the union of the files is kept, everything else is uninstalled.
Preview before applying with pip-sync --dry-run, or use pip-sync --ask for interactive confirmation.
Official docs: https://pip-tools.readthedocs.io/en/stable/
Known gotchas
pip-sync uninstalls aggressively: anything installed in the env but absent from the given requirement files is removed. Run --dry-run first in shared or long-lived environments.
pip-compile does not generate hashes by default; add --generate-hashes if you want hash-checked installs.
Transitive dependencies appear only in requirements.txt, not requirements.in. Never hand-edit requirements.txt — regenerate it from the .in file, or edits are lost on the next compile.
By default pip-compile does not upgrade already-pinned versions in an existing requirements.txt; use --upgrade (all) or -P <pkg> (one) to move pins.
pip-sync is designed for requirements.txt files produced by pip-compile with fully pinned == versions; feeding it loose specifiers defeats determinism.
Make sure pip-sync and CI use the same index configuration (--index-url/--find-links) as pip-compile did, or resolution results can differ.
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