Contributing to Scrapy¶

Important

Double check that you are reading the most recent version of this document at https://docs.scrapy.org/en/master/contributing.html

There are many ways to contribute to Scrapy. Here are some of them:

Report bugs and request features in the issue tracker, trying to follow the guidelines detailed in Reporting bugs below.
Submit patches for new functionalities and/or bug fixes. Please read Writing patches and Submitting patches below for details on how to write and submit a patch.
Blog about Scrapy. Tell the world how you’re using Scrapy. This will help newcomers with more examples and will help the Scrapy project to increase its visibility.
Join the Scrapy subreddit and share your ideas on how to improve Scrapy. We’re always open to suggestions.
Answer Scrapy questions at Stack Overflow.

Reporting bugs¶

Note

Please report security issues only to scrapy-security@googlegroups.com. This is a private list only open to trusted Scrapy developers, and its archives are not public.

Well-written bug reports are very helpful, so keep in mind the following guidelines when you’re going to report a new bug.

check the FAQ first to see if your issue is addressed in a well-known question
if you have a general question about Scrapy usage, please ask it at Stack Overflow (use “scrapy” tag).
check the open issues to see if the issue has already been reported. If it has, don’t dismiss the report, but check the ticket history and comments. If you have additional useful information, please leave a comment, or consider sending a pull request with a fix.
search the scrapy-users list and Scrapy subreddit to see if it has been discussed there, or if you’re not sure if what you’re seeing is a bug. You can also ask in the #scrapy IRC channel.
write complete, reproducible, specific bug reports. The smaller the test case, the better. Remember that other developers won’t have your project to reproduce the bug, so please include all relevant files required to reproduce it. See for example StackOverflow’s guide on creating a Minimal, Complete, and Verifiable example exhibiting the issue.
the most awesome way to provide a complete reproducible example is to send a pull request which adds a failing test case to the Scrapy testing suite (see Submitting patches). This is helpful even if you don’t have an intention to fix the issue yourselves.
include the output of scrapy version -v so developers working on your bug know exactly which version and platform it occurred on, which is often very helpful for reproducing it, or knowing if it was already fixed.

Finding work¶

If you have decided to make a contribution to Scrapy, but you do not know what to contribute, you have a few options to find pending work:

Check out the contribution GitHub page, which lists open issues tagged as good first issue.

There are also help wanted issues but mind that some may require familiarity with the Scrapy code base. You can also target any other issue provided it is not tagged as discuss.
If you enjoy writing documentation, there are documentation issues as well, but mind that some may require familiarity with the Scrapy code base as well.
If you enjoy writing automated tests, you can work on increasing our test coverage.
If you enjoy code cleanup, we welcome fixes for issues detected by our static analysis tools. See pyproject.toml for silenced issues that may need addressing.

Mind that some issues we do not aim to address at all, and usually include a comment on them explaining the reason; not to confuse with comments that state what the issue is about, for non-descriptive issue codes.

If you have found an issue, make sure you read the entire issue thread before you ask questions. That includes related issues and pull requests that show up in the issue thread when the issue is mentioned elsewhere.

We do not assign issues, and you do not need to announce that you are going to start working on an issue either. If you want to work on an issue, just go ahead and write a patch for it.

Do not discard an issue simply because there is an open pull request for it. Check if open pull requests are active first. And even if some are active, if you think you can build a better implementation, feel free to create a pull request with your approach.

If you decide to work on something without an open issue, please:

Do not create an issue to work on code coverage or code cleanup, create a pull request directly.
Do not create both an issue and a pull request right away. Either open an issue first to get feedback on whether or not the issue is worth addressing, and create a pull request later only if the feedback from the team is positive, or create only a pull request, if you think a discussion will be easier over your code.
Do not add docstrings for the sake of adding docstrings, or only to address silenced Ruff issues. We expect docstrings to exist only when they add something significant to readers, such as explaining something that is not easier to understand from reading the corresponding code, summarizing a long, hard-to-read implementation, providing context about calling code, or indicating purposely uncaught exceptions from called code.
Do not add tests that use as much mocking as possible just to touch a given line of code and hence improve line coverage. While we do aim to maximize test coverage, tests should be written for real scenarios, with minimum mocking. We usually prefer end-to-end tests.

Writing patches¶

The better a patch is written, the higher the chances that it’ll get accepted and the sooner it will be merged.

Well-written patches should:

contain the minimum amount of code required for the specific change. Small patches are easier to review and merge. So, if you’re doing more than one change (or bug fix), please consider submitting one patch per change. Do not collapse multiple changes into a single patch. For big changes consider using a patch queue.
pass all unit-tests. See Running tests below.
include one (or more) test cases that check the bug fixed or the new functionality added. See Writing tests below.
if you’re adding or changing a public (documented) API, please include the documentation changes in the same patch. See Documentation policies below.
if you’re adding a private API, please add a regular expression to the coverage_ignore_pyobjects variable of docs/conf.py to exclude the new private API from documentation coverage checks.

To see if your private API is skipped properly, generate a documentation coverage report as follows:
```
tox -e docs-coverage
```
if you are removing deprecated code, first make sure that at least 1 year (12 months) has passed since the release that introduced the deprecation. See Deprecation policy.

Submitting patches¶

The best way to submit a patch is to issue a pull request on GitHub, optionally creating a new issue first.

Remember to explain what was fixed or the new functionality (what it is, why it’s needed, etc). The more info you include, the easier will be for core developers to understand and accept your patch.

If your pull request aims to resolve an open issue, link it accordingly, e.g.:

Resolves #123

You can also discuss the new functionality (or bug fix) before creating the patch, but it’s always good to have a patch ready to illustrate your arguments and show that you have put some additional thought into the subject. A good starting point is to send a pull request on GitHub. It can be simple enough to illustrate your idea, and leave documentation/tests for later, after the idea has been validated and proven useful. Alternatively, you can start a conversation in the Scrapy subreddit to discuss your idea first.

Sometimes there is an existing pull request for the problem you’d like to solve, which is stalled for some reason. Often the pull request is in a right direction, but changes are requested by Scrapy maintainers, and the original pull request author hasn’t had time to address them. In this case consider picking up this pull request: open a new pull request with all commits from the original pull request, as well as additional changes to address the raised issues. Doing so helps a lot; it is not considered rude as long as the original author is acknowledged by keeping his/her commits.

You can pull an existing pull request to a local branch by running git fetch upstream pull/$PR_NUMBER/head:$BRANCH_NAME_TO_CREATE (replace ‘upstream’ with a remote name for scrapy repository, $PR_NUMBER with an ID of the pull request, and $BRANCH_NAME_TO_CREATE with a name of the branch you want to create locally). See also: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally#modifying-an-inactive-pull-request-locally.

When writing GitHub pull requests, try to keep titles short but descriptive. E.g. For bug #411: “Scrapy hangs if an exception raises in start_requests” prefer “Fix hanging when exception occurs in start_requests (#411)” instead of “Fix for #411”. Complete titles make it easy to skim through the issue tracker.

Finally, try to keep aesthetic changes (PEP 8 compliance, unused imports removal, etc) in separate commits from functional changes. This will make pull requests easier to review and more likely to get merged.

Coding style¶

Please follow these coding conventions when writing code for inclusion in Scrapy:

We use black for code formatting. There is a hook in the pre-commit config that will automatically format your code before every commit. You can also run black manually with tox -e pre-commit.
Don’t put your name in the code you contribute; git provides enough metadata to identify author of the code. See https://docs.github.com/en/get-started/getting-started-with-git/setting-your-username-in-git for setup instructions.

Pre-commit¶

We use pre-commit to automatically address simple code issues before every commit.

After your create a local clone of your fork of the Scrapy repository:

Install pre-commit.
On the root of your local clone of the Scrapy repository, run the following command:
```
pre-commit install
```

Now pre-commit will check your changes every time you create a Git commit. Upon finding issues, pre-commit aborts your commit, and either fixes those issues automatically, or only reports them to you. If it fixes those issues automatically, creating your commit again should succeed. Otherwise, you may need to address the corresponding issues manually first.

Documentation policies¶

For reference documentation of API members (classes, methods, etc.) use docstrings and make sure that the Sphinx documentation uses the autodoc extension to pull the docstrings. API reference documentation should follow docstring conventions (PEP 257) and be IDE-friendly: short, to the point, and it may provide short examples.

Other types of documentation, such as tutorials or topics, should be covered in files within the docs/ directory. This includes documentation that is specific to an API member, but goes beyond API reference documentation.

In any case, if something is covered in a docstring, use the autodoc extension to pull the docstring into the documentation instead of duplicating the docstring in files within the docs/ directory.

Documentation updates that cover new or modified features must use Sphinx’s versionadded and versionchanged directives. Use VERSION as version, we will replace it with the actual version right before the corresponding release. When we release a new major or minor version of Scrapy, we remove these directives if they are older than 3 years.

Documentation about deprecated features must be removed as those features are deprecated, so that new readers do not run into it. New deprecations and deprecation removals are documented in the release notes.

Tests¶

Tests are implemented using the Twisted unit-testing framework. Running tests requires tox.

Running tests¶

To run all tests:

tox

To run a specific test (say tests/test_loader.py) use:

tox -- tests/test_loader.py

To run the tests on a specific tox environment, use -e <name> with an environment name from tox.ini. For example, to run the tests with Python 3.10 use:

tox -e py310

You can also specify a comma-separated list of environments, and use tox’s parallel mode to run the tests on multiple environments in parallel:

tox -e py39,py310 -p auto

To pass command-line options to pytest, add them after -- in your call to tox. Using -- overrides the default positional arguments defined in tox.ini, so you must include those default positional arguments (scrapy tests) after -- as well:

tox -- scrapy tests -x  # stop after first failure

You can also use the pytest-xdist plugin. For example, to run all tests on the Python 3.10 tox environment using all your CPU cores:

tox -e py310 -- scrapy tests -n auto

To see coverage report install coverage (pip install coverage) and run:

coverage report

see output of coverage --help for more options like html or xml report.

Writing tests¶

All functionality (including new features and bug fixes) must include a test case to check that it works as expected, so please include tests for your patches if you want them to get accepted sooner.

Scrapy uses unit-tests, which are located in the tests/ directory. Their module name typically resembles the full path of the module they’re testing. For example, the item loaders code is in:

scrapy.loader

And their unit-tests are in:

tests/test_loader.py