Compile multiple requirements files to lock dependency versions
Compile multiple requirements files to lock dependency versions
pip install pip-compile-multi
I will start from the very basics of dependency management and will go very slow, so if you feel bored, just scroll to the next section.
Suppose you have a python project with following direct dependencies:
(Yes I took pip-compile-multi as an example). Let’s save them as-is in requirements/base.in. Those are unpinned libraries. It means that whenever developer runs
pip install -r requirements/base.in
they will get some version of these libraries. And the chances are that if several developers do the same over some period, some will have different dependency versions than others. Also, if the project is online service, one day it may stop working after redeployment because some of the dependencies had backward incompatible release. These backward incompatible changes are relatively common.
To avoid this problem, Python developers are hard-pinning (aka locking) their dependencies. So instead of a list of libraries, they have something like:
(To keep things neat let’s put this into requirements/base.txt) That’s good for a starter. But there are two significant drawbacks:
- Developers have to do non-trivial operations if they want to keep up with newer versions (that have bug fixes and performance improvements).
- Indirect dependencies (that is dependencies of dependencies) may still have backward-incompatible releases, that break everything.
Let’s put aside point 1 and fight point 2. Let’s do
pip freeze > requirements/base.txt
Now we have full hierarchy of dependencies hard-pinned:
click==6.7 first==2.0.1 pip-tools==1.11.0 six==1.11.0
That’s great, and solves the main problem - service will be deployed exactly  the same every single time and all developers will have same environments.
This case is so common that there already are some tools to solve it. Two worth mentioning are:
- Pip Tools - a mature package that is enhanced by pip-compile-multi.
- PipEnv - a fresh approach that is going to become the “official” Python way of locking dependencies some day.
But what if the project uses some packages that are not required by the service itself? For example pytest, that is needed to run unit tests, but should never be deployed to a production site. Or flake8 - syntax checking tool. If they are installed in the current virtual environment, they will get into pip freeze output. That’s no good. And removing them manually from requirements/base.txt is not an option. But still, these packages must be pinned to ensure, that tests are running the same way on all development machines (and build server).
So let’s get hands dirty and put all the testing stuff into requirements/test.in:
-r base.in prospector pylint flake8 mock six
Note, how I put -r base.in in the beginning, so that test dependencies are installed along with the base.
Now installation command is
pip install -e requirements/test.in
For one single time (exceptionally to show how unacceptable is this task) let’s manually compose requirements/test.txt. After installation, run freeze to bring the whole list of all locked packages:
$ pip freeze astroid==1.6.0 click==6.7 dodgy==0.1.9 first==2.0.1 flake8==3.5.0 flake8-polyfill==1.0.2 isort==4.2.15 lazy-object-proxy==1.3.1 mccabe==0.6.1 mock==2.0.0 pbr==3.1.1 pep8-naming==0.5.0 pip-tools==1.11.0 prospector==0.12.7 pycodestyle==2.0.0 pydocstyle==2.1.1 pyflakes==1.6.0 pylint==1.8.1 pylint-celery==0.3 pylint-common==0.2.5 pylint-django==0.7.2 pylint-flask==0.5 pylint-plugin-utils==0.2.6 PyYAML==3.12 requirements-detector==0.5.2 setoptconf==0.2.0 six==1.11.0 snowballstemmer==1.2.1 wrapt==1.10.11
Wow! That’s quite a list! But we remember what goes into base.txt:
Good, everything else can be put into requirements/test.txt. But wait, six is included in test.in and is missing in test.txt. That feels wrong. Ah, it’s because we’ve moved six to the base.txt. It’s good that we didn’t forget, that it should be in base. We might forget next time though.
Why don’t we automate it? That’s what pip-compile-multi is for.
Managing dependency versions in multiple environments
Let’s rehearse. Example service has two groups of dependencies (or, as I call them, environments):
$ cat requirements/base.in click pip-tools $ cat requirements/test.in -r base.in prospector pylint flake8 mock six
To make automation even more appealing, let’s add one more environment. I’ll call it local - things that are needed during development, but are not required by tests, or service itself.
$ cat requirements/local.in -r test.in tox
Now we want to put all base dependencies along with all their recursive dependencies in base.txt, all recursive test dependencies except for base into test.txt, and all recursive local dependencies except for base and test into local.txt.
$ pip-compile-multi Locking requirements/base.in to requirements/base.txt. References:  Locking requirements/test.in to requirements/test.txt. References: ['base'] Locking requirements/local.in to requirements/local.txt. References: ['base', 'test']
Yes, that’s right. All the tedious dependency versions management job done with a single command that doesn’t even have options.
Now you can run git diff to review the changes and git commit to save them. To install the new set of versions run:
pip install -Ur requirements/local.txt
It’s a perfect time to run all the tests and make sure, that updates were backward compatible enough for your needs. More often than I’d like in big projects, it’s not so. Let’s say the new version of pylint dropped support of old Python version, that you still need to support. Than you open test.in and soft-pin it with descriptive comment:
$ cat requirements/test.in -r base.in prospector pylint<1.8 # Newer versions dropped support for Python 2.4 flake8 mock six
I know, this example is made up. But you get the idea. That re-run pip-compile-multi to compile new test.txt and check new set.
Benefits of using pip-compile-multi
I want to summarise, why pip-compile-multi might be a good addition to your project. Some of the benefits are achievable with other methods, but I want to be general:
- Production will not suddenly break after redeployment because of backward incompatible dependency release.
- Every development machine will have the same package versions.
- Service still uses most recent versions of packages. And fresh means best here.
- Dependencies are upgraded when the time is suitable for the service, not whenever they are released.
- Different environments are separated into different files.
- *.in files are small and manageable because they store only direct dependencies.
- *.txt files are exhaustive and precise (but you don’t need to edit them).
pip-compile-multi supports many options to customize compilation.
While it’s a common practice to put requirements files inside requirements directory, it’s not always the case. The directory can be overridden with this option:
-d, --directory TEXT Directory path with requirements files
Requirements Files Extensions
By default pip-compile-multi compiles *.txt from *.in files. While this is a common naming pattern, each project can use it’s own:
-i, --in-ext TEXT File extension of input files -o, --out-ext TEXT File extension of output files
When new dependencies are added it’s tempting to keep everything else the same. To recompile .txt keeping satisfying version use --no-upgrade:
--upgrade / --no-upgrade Upgrade package version (default true)
The option does not affect if there are no existing .txt files.
PEP-440 describes compatible release operator ~=. Sometimes it’s useful to have some of the dependencies pinned using this operator. For example, rapidly changing internal libraries. The format for this option is
-c, --compatible TEXT
where TEXT is a glob pattern for library name. This option can be supplied multiple times.
Put package hash after pinned version for additional security. Format for this option is
-g, --generate-hashes TEXT Environment name (base, test, etc.) that needs packages hashes. Can be supplied multiple times.
$ pip-compile-multi -g base -g docs
pip-tools==1.11.0 \ --hash=sha256:50288eb066ce66dbef5401a21530712a93c659fe480c7d8d34e2379300555fa1 \ --hash=sha256:ba427b68443466c389e3b0b0ef55f537ab39344190ea980dfebb333d0e6a50a3 first==2.0.1 \ --hash=sha256:3bb3de3582cb27071cfb514f00ed784dc444b7f96dc21e140de65fe00585c95e \ --hash=sha256:41d5b64e70507d0c3ca742d68010a76060eea8a3d863e9b5130ab11a4a91aa0e \ # via pip-tools
pip requires all packages to have hashes if at least one has it. pip-compile-multi will recursively propagate this option to all environments that are referencing or referenced by selected environment name.
pip-compile-multi adds a brief header into generated files. Override it with
-h, --header TEXT File path with custom header text for generated files
Limit .in files
By default pip-compile-multi compiles all .in files in requirements directory. To limit compilation to only a subset, use
-n, --only-name TEXT Compile only for passed environment names and their references. Can be supplied multiple times.
For example, to compile one file under Python2.7 and another under Python3.6, run:
$ virtual-env27/bin/pip-compile-multi -n deps27 Locking requirements/deps27.in to requirements/deps27.txt. References:  $ virtual-env36/bin/pip-compile-multi -n deps36 Locking requirements/deps36.in to requirements/deps36.txt. References: 
Forbid .postX release
pip-compile-multi can remove .postX part of dependencies versions.
-P, --forbid-post TEXT Environment name (base, test, etc) that cannot have packages with post-release versions (1.2.3.post777). Can be supplied multiple times.
Be careful with this option since different maintainers treat post releases differently.
Check that pip-compile-multi was run after changes in .in file.
pip-compile-multi adds a special line (before header) at the beginning of each generated file. This line contains a SHA1 hash of the .in file’s contents.
$ pip-compile-multi verify Verifying that requirements/base.txt was generated from requirements/base.in. Success - comments match. Verifying that requirements/test.txt was generated from requirements/test.in. Success - comments match. Verifying that requirements/local.txt was generated from requirements/local.in. Success - comments match.
recalculates hashes for .in files and compares them with the stored values.
If verification fails, an error message is logged and exit code 1 is returned:
$ pip-compile-multi verify Verifying that requirements/base.txt was generated from requirements/base.in. Success - comments match. Verifying that requirements/test.txt was generated from requirements/test.in. FAILURE! Expecting: # SHA1:c93d71964e14b04f3c8327d16dbc4d6b1bbc3b1d Found: # SHA1:6c2562322ca1bdc8309b08581a2aa4efbb5a4534 Verifying that requirements/local.txt was generated from requirements/local.in. Success - comments match.
In big teams it might be a good idea to have this check in tox.ini:
[testenv:deps] skip_install = True deps = pip-compile-multi commands = pip-compile-multi verify
Verify as pre-commit hook
To verify that pip-compile-multi has been run after changing .in files as a PreCommit hook, just add the following to your local repo’s .pre-commit-config.yaml file:
- repo: https://github.com/peterdemin/pip-compile-multi rev: v1.3.2 hooks: - id: pip-compile-multi-verify
Bonus: boilerplate to put in project’s README
Nice way of introducing dependency management process to new team members for copy-pasting to README.md:
## Dependency management This project uses [pip-compile-multi](https://pypi.org/project/pip-compile-multi/) for hard-pinning dependencies versions. Please see its documentation for usage instructions. In short, `requirements/base.in` contains the list of direct requirements with occasional version constraints (like `Django<2`) and `requirements/base.txt` is automatically generated from it by adding recursive tree of dependencies with fixed versions. The same goes for `test` and `dev`. To upgrade dependency versions, run `pip-compile-multi`. To add a new dependency without upgrade, add it to `requirements/base.in` and run `pip-compile-multi --no-upgrade`. For installation always use `.txt` files. For example, command `pip install -Ue . -r requirements/dev.txt` will install this project in development mode, testing requirements and development tools. Another useful command is `pip-sync requirements/dev.txt`, it uninstalls packages from your virtualenv that aren't listed in the file.
Now that occasional backward incompatible dependency release can’t ruin your day, you can spread the word about pip-compile-multi, ask for a new feature in a GitHub issue, or even open a PR ;-).
 That’s not true. Someone could re-upload broken package under existing version on PyPI.
- Re-remove workaround for future[s] packages in Python3
- Introduced CLI v2 (disabled by default)
- Remove workaround for future[s] packages in Python3 (no longer needed)
- Fixed Restructured text formatting (thanks to @yigor)
- Updated test dependencies (and hashes)
- Added –forbid-post option
- Added checks for conflicting package versions
- Added support for VCS dependencies
- Added –no-upgrade option
- Propagate –only-name option to references
- Fixed extension override options
- Added --generate-hashes option
- Fixed directory override option
- Added –only-name option
- Fixed comment justification
- Added pip-compile-multi verify command
- Omit future[s] packages for Python3
- Added files discovery.
- First release on PyPI.
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