formatters.rst

Developing a Formatting Plugin for Flake8

allowed for custom formatting plugins in version 3.0.0. Let's write a plugin together:

from flake8.formatting import base


class Example(base.BaseFormatter):
    """Flake8's example formatter."""

    pass

We notice, as soon as we start, that we inherit from 's ~flake8.formatting.base.BaseFormatter class. If we follow the instructions to register a plugin <register-a-plugin> and try to use our example formatter, e.g., flake8 --format=example then will fail because we did not implement the format method. Let's do that next.

class Example(base.BaseFormatter):
    """Flake8's example formatter."""

    def format(self, error):
        return 'Example formatter: {0!r}'.format(error)

With that we're done. Obviously this isn't a very useful formatter, but it should highlight the simplicity of creating a formatter with Flake8. If we wanted to instead create a formatter that aggregated the results and returned XML, JSON, or subunit we could also do that. interacts with the formatter in two ways:

1. It creates the formatter and provides it the options parsed from the configuration files and command-line
2. It uses the instance of the formatter and calls handle with the error.

By default flake8.formatting.base.BaseFormatter.handle simply calls the format method and then write. Any extra handling you wish to do for formatting purposes should override the handle method.

API Documentation

flake8.formatting.base.BaseFormatter