# Documentation

Documentation is incredibly important to Prefect, both for explaining its concepts to general audiences and describing its API to developers.

# Docstrings

Prefect auto-generates API documentation from docstrings by compiling them to Markdown. For details on properly formatting your docstrings, please see the code style guide.

# API Reference

Modules, functions, and classes must be explicitly added to the auto-generated documentation. First, update the docs/outline.toml file with the following information:

  • a TOML header with the path to the generated Markdown file (e.g. pages.utilities.example)
  • title (str): the title of the generated docs page
  • module (str, optional): the import path to the module being documented. The module docstring will be displayed at the top of the page.
  • classes (list or dict, optional): a list of class names in module to document (all public methods of these classes will be documented). Alternatively, a dict mapping class names to lists of method names to document can be used (only explicitly listed method names will be documented).
  • functions (list, optional): a list of function names in module to document

For example, to document a module prefect.utilities.example with a class MyClass and a function my_function, you might add the following to outline.toml:

title = "Example Module"
module = "prefect.utilities.example"
classes = ["MyClass"]
functions = ["my_function"]

Most reference docs sections update their sidebars automatically by detecting the files generated from outline.toml. However, in some instances you may have to include your file explicitly. To do so, update docs/.vuepress/config.js and add it to the appropriate "children" section. The actual prefect.utilities section does auto-update its sidebar, but for the sake of example, you would add the new file to the children array like so:

    title: 'prefect.utilities',
    collapsable: true,
    children: [
        'utilities/example',  // our new file

# Archiving API docs

Whenever a new minor release of Prefect is cut, we must archive the old API docs so they are available for users using the older versions. For example, this means that if we are releasing Prefect 0.10.0 then the highest patch release of 0.9.x must be archived. To do so, follow these steps:

  • first, make sure you are on the release commit: git checkout $VERSION_TAG
  • next, generate the documentation: cd docs/ && python generate_docs.py
  • push the API docs into a new folder: cd api/ && mv latest/ $VERSION_TAG
  • begin tracking any changes to the new folder: git checkout master && git checkout -b new-version-branch && git add $VERSION_TAG
  • lastly, create a new sidebar.js file in the $VERSION_TAG/ folder with an exportable sidebar object (see 0.11.5 for an example)
  • this sidebar will need to be imported into docs/.vuepress/config.js and added to a new dropdown option in the API navigation bar

The most recent release of Prefect will always be the latest release and the API docs for latest are auto generated with each doc build. On release the Latest (x.y.z) should be updated with the most recent version in docs/.vuepress/config.js.

# Concepts

Prefect also includes a great deal of "concept" documentation, which covers features, tutorials, guides, and examples separately from the auto-generated API reference. This page is part of the concept documentation for development! We refer to non-API documentation as Prefect's "Guide".

To write concept docs, add Markdown files to the docs/guide directory (or one of its subdirectories). To ensure that your page is displayed in the navigation, edit docs/.vuepress/config.js to include a reference to it.

# Semantics

# Capitalization

Concepts that refer to proper nouns or are trademarked should always be capitalized, including "Prefect", "Core" (when referring to Prefect Core), and "Cloud" (when referring to Prefect Cloud).

Other Prefect terms, like "flow" or "task", should generally not be capitalized unless they refer to a specific Python class. For example:

When a flow is run, its tasks are executed in sequence. Each Task has a trigger function that determines if it should run.

To execute a Flow, call its .run() method.

In order to manage data serialization, users can specify one or more ResultHandlers for their flows and tasks.

Prefect uses a rich state system to communicate information between tasks. Each State has multiple attributes, including an informative message.

# Previewing docs locally

Documentation (including both concepts and API references) is built and deployed with every merge to Prefect's master branch. Prior to merge, a GitHub check will allow you to see a hosted version of the documentation associated with every PR.

To preview docs locally, you'll first need to install VuePress and its dependencies. This requires Node.js and npm (which is installed with Node.js). You will also need to install the rest of Prefect's dependencies for generating docs. You only need to do this once:

git clone https://github.com/PrefectHQ/prefect.git
cd prefect
npm install
pip install ".[all_extras]"

To launch a documentation preview:

cd prefect
npm run docs:dev

You'll see a status update as the docs build, and then an announcement that they are available on http://localhost:8080.

Hot-reloading docs

Concept docs will hot-reload every time you save a file, but API reference docs must be regenerated by restarting the server.