Now that you have a directory layout, you can declare the project’s requirements.
The requirements of applications (not packages) are managed by four files:
requirements.innames all direct requirements needed in the production environment, i.e. all packages
import’ed by the application.
If the application is incompatible with older or newer versions of a requirement, use the least specific version specifier possible, for example:
requirements_dev.innames all direct requirements needed exclusively in the development environment, and not in the production environment, e.g.
This file should include the direct requirements needed in the production environment, by having a first line of
requirements.txtnames all direct and indirect requirements needed in the production environment, all locked to specific versions by pip-tools.
requirements_dev.txtnames all direct and indirect requirements needed in the development environment, all locked to specific versions by
This ensures that:
All environments use the same versions of production requirements, to ensure consistent and replicable deployments and to avoid errors or surprises during or after deployment due to differences between versions (e.g. a new version of Django requires upgrading application code).
Different developers and continuous integration use the same versions of development requirements, to avoid test failures due to differences between versions (e.g. a new version of pytest requires upgrading test code, or a new version of flake8 has stricter linting rules).
pip install pip-tools
A common starter
requirements.in for Django is:
dj-database-url django psycopg2 sentry-sdk
A common starter
requirements_dev.in for linting in Django is:
-r requirements.txt black coverage coveralls flake8 isort pip-tools pre-commit
If not using Django, remove
coverage and add:
Add a requirement#
Add the requirement in alphabetical order to the appropriate
.in file. Then, run:
pip-compile pip-compile requirements_dev.in
pip-compile introduces unexpected differences, upgrade
pip-tools to the latest version, and check that you are using the same version of Python as for other runs.
psycopg2 is recommended for production. However, installing
psycopg2 for development can be difficult on operating systems like macOS. In that case, you can:
pip install psycopg2-binary
You must keep the locked versions of psycopg2 and psycopg2-binary in sync.
pip-sync -q --pip-args "--exists-action w"
Requirements should be periodically updated, both for security updates and to better distribute the maintenance burden of upgrading versions over time.
Upgrade one requirement, for example:
pip-compile -P requests pip-compile -P requests requirements_dev.in
Upgrade all requirements:
pip-compile --upgrade pip-compile --upgrade requirements_dev.in