(Instructions for aiohttp admins)

Instructions for contributors

In order to make a clone of the GitHub repo: open the link and press the “Fork” button on the upper-right menu of the web page.

I hope everybody knows how to work with git and github nowadays :)

Workflow is pretty straightforward:

  1. Make sure you are reading the latest version of this document. It can be found in the GitHub repo in the docs subdirectory.

  2. Clone the GitHub repo using the --recurse-submodules argument

  3. Setup your machine with the required development environment

  4. Make a change

  5. Make sure all tests passed

  6. Add a file into the CHANGES folder (see Changelog update for how).

  7. Commit changes to your own aiohttp clone

  8. Make a pull request from the github page of your clone against the master branch

  9. Optionally make backport Pull Request(s) for landing a bug fix into released aiohttp versions.


The project uses Squash-and-Merge strategy for GitHub Merge button.

Basically it means that there is no need to rebase a Pull Request against master branch. Just git merge master into your working copy (a fork) if needed. The Pull Request is automatically squashed into the single commit once the PR is accepted.


GitHub issue and pull request threads are automatically locked when there has not been any recent activity for one year. Please open a new issue for related bugs.

If you feel like there are important points in the locked discussions, please include those excerpts into that new issue.

Preconditions for running aiohttp test suite

We expect you to use a python virtual environment to run our tests.

There are several ways to make a virtual environment.

If you like to use virtualenv please run:

$ cd aiohttp
$ virtualenv --python=`which python3` venv
$ . venv/bin/activate

For standard python venv:

$ cd aiohttp
$ python3 -m venv venv
$ . venv/bin/activate

For virtualenvwrapper:

$ cd aiohttp
$ mkvirtualenv --python=`which python3` aiohttp

There are other tools like pyvenv but you know the rule of thumb now: create a python3 virtual environment and activate it.

After that please install libraries required for development:

$ make install-dev


For now, the development tooling depends on make and assumes an Unix OS If you wish to contribute to aiohttp from a Windows machine, the easiest way is probably to configure the WSL so you can use the same instructions. If it’s not possible for you or if it doesn’t work, please contact us so we can find a solution together.

Install pre-commit hooks:

$ pre-commit install


If you plan to use temporary print(), pdb or ipdb within the test suite, execute it with -s:

$ pytest tests -s

in order to run the tests without output capturing.

Congratulations, you are ready to run the test suite!


When building aiohttp from source, there is a pure Python parser used by default. For better performance, you may want to build the higher performance C parser.

To build this llhttp parser, first get/update the submodules (to update to a newer release, add --remote):

git submodule update --init --recursive

Then build llhttp:

cd vendor/llhttp/
npm install

Then build our parser:

cd -
make cythonize

Then you can build or install it with python -m build or pip install -e .

Run autoformatter

The project uses black + isort formatters to keep the source code style. Please run make fmt after every change before starting tests.

$ make fmt

Run aiohttp test suite

After all the preconditions are met you can run tests typing the next command:

$ make test

The command at first will run the linters (sorry, we don’t accept pull requests with pyflakes, black, isort, or mypy errors).

On lint success the tests will be run.

Please take a look on the produced output.

Any extra texts (print statements and so on) should be removed.


If you see that CI build is failing on a specific Python version and you don’t have this version on your computer, you can use the helper to run it (only if you have docker):

make test-<python-version>[-no-extensions]

For example, if you want to run tests for python3.10 without extensions, you can run this command:

make test-3.10-no-extensions

Tests coverage

We are trying hard to have good test coverage; please don’t make it worse.


$ make cov-dev

to run test suite and collect coverage information. Once the command has finished check your coverage at the file that appears in the last line of the output: open file:///.../aiohttp/htmlcov/index.html

Please go to the link and make sure that your code change is covered.

The project uses for storing coverage results. Visit for looking on coverage of master branch, history, pull requests etc.

The browser extension is highly recommended for analyzing the coverage just in Files Changed tab on GitHub Pull Request review page.


We encourage documentation improvements.

Please before making a Pull Request about documentation changes run:

$ make doc

Once it finishes it will output the index html page open file:///.../aiohttp/docs/_build/html/index.html.

Go to the link and make sure your doc changes looks good.

Spell checking

We use pyenchant and sphinxcontrib-spelling for running spell checker for documentation:

$ make doc-spelling

Unfortunately there are problems with running spell checker on MacOS X.

To run spell checker on Linux box you should install it first:

$ sudo apt-get install enchant
$ pip install sphinxcontrib-spelling

Changelog update

The CHANGES.rst file is managed using towncrier tool and all non trivial changes must be accompanied by a news entry.

To add an entry to the news file, first you need to have created an issue describing the change you want to make. A Pull Request itself may function as such, but it is preferred to have a dedicated issue (for example, in case the PR ends up rejected due to code quality reasons).

Once you have an issue or pull request, you take the number and you create a file inside of the CHANGES/ directory named after that issue number with an extension of .removal, .feature, .bugfix, or .doc. Thus if your issue or PR number is 1234 and this change is fixing a bug, then you would create a file CHANGES/1234.bugfix. PRs can span multiple categories by creating multiple files (for instance, if you added a feature and deprecated/removed the old feature at the same time, you would create CHANGES/NNNN.feature and CHANGES/NNNN.removal). Likewise if a PR touches multiple issues/PRs you may create a file for each of them with the exact same contents and Towncrier will deduplicate them.

The contents of this file are reStructuredText formatted text that will be used as the content of the news file entry. You do not need to reference the issue or PR numbers here as towncrier will automatically add a reference to all of the affected issues when rendering the news file.

Making a Pull Request

After finishing all steps make a GitHub Pull Request with master base branch.


All Pull Requests are created against master git branch.

If the Pull Request is not a new functionality but bug fixing backport to maintenance branch would be desirable.

aiohttp project committer may ask for making a backport of the PR into maintained branch(es), in this case he or she adds a github label like needs backport to 3.1.

Backporting is performed after main PR merging into master.

Please do the following steps:

  1. Find Pull Request’s commit for cherry-picking.

    aiohttp does squashing PRs on merging, so open your PR page on github and scroll down to message like asvetlov merged commit f7b8921 into master 9 days ago. f7b8921 is the required commit number.

  2. Run cherry_picker tool for making backport PR (the tool is already pre-installed from ./requirements/dev.txt), e.g. cherry_picker f7b8921 3.1.

  3. In case of conflicts fix them and continue cherry-picking by cherry_picker --continue.

    cherry_picker --abort stops the process.

    cherry_picker --status shows current cherry-picking status (like git status)

  4. After all conflicts are done the tool opens a New Pull Request page in a browser with pre-filed information. Create a backport Pull Request and wait for review/merging.

  5. aiohttp committer should remove backport Git label after merging the backport.

How to become an aiohttp committer


The easiest way is providing Pull Requests for issues in our bug tracker. But if you have a great idea for the library improvement – please make an issue and Pull Request.

The rules for committers are simple:

  1. No wild commits! Everything should go through PRs.

  2. Take a part in reviews. It’s very important part of maintainer’s activity.

  3. Pickup issues created by others, especially if they are simple.

  4. Keep test suite comprehensive. In practice it means leveling up coverage. 97% is not bad but we wish to have 100% someday. Well, 99% is good target too.

  5. Don’t hesitate to improve our docs. Documentation is a very important thing, it’s the key for project success. The documentation should not only cover our public API but help newbies to start using the project and shed a light on non-obvious gotchas.

After positive answer aiohttp committer creates an issue on github with the proposal for nomination. If the proposal will collect only positive votes and no strong objection – you’ll be a new member in our team.