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3.9 KiB
ReStructuredText
130 lines
No EOL
3.9 KiB
ReStructuredText
Writing an Extension for Flake8
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===============================
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Since Flake8 is now adding support for extensions, we require ``setuptools``
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so we can manage extensions through entry points. If you are making an
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existing tool compatible with Flake8 but do not already require
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``setuptools``, you should probably add it to your list of requirements. Next,
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you'll need to edit your ``setup.py`` file so that upon installation, your
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extension is registered. If you define a class called ``PackageEntryClass``
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then this would look something like the following::
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setup(
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# ...
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entry_points={
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'flake8.extension': ['P10 = package.PackageEntryClass'],
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}
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# ...
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)
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If you intend to publish your extension, choose a unique code prefix
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following the convention for :ref:`error codes <error-codes>`.
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In addition, you can open a request in the `issue tracker
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<https://bitbucket.org/tarek/flake8/issues>`_ to register the prefix in the
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documentation.
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.. TODO: describe the API required for the 3 kind of extensions:
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* physical line checkers
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* logical line checkers
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* AST checkers
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A real example: McCabe
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----------------------
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Below is an example from mccabe_ for how to write your ``setup.py`` file for
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your Flake8 extension.
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.. code-block:: python
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# https://github.com/flintwork/mccabe/blob/0.2/setup.py#L38:L42
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# -*- coding: utf-8 -*-
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from setuptools import setup
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# ...
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setup(
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name='mccabe',
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# ...
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install_requires=[
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'setuptools',
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],
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entry_points={
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'flake8.extension': [
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'C90 = mccabe:McCabeChecker',
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],
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},
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# ...
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)
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In ``mccabe.py`` you can see that extra options are added to the parser when
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flake8 registers the extension:
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.. code-block:: python
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# https://github.com/flintwork/mccabe/blob/0.2/mccabe.py#L225:L254
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class McCabeChecker(object):
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"""McCabe cyclomatic complexity checker."""
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name = 'mccabe'
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version = __version__
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_code = 'C901'
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_error_tmpl = "C901 %r is too complex (%d)"
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max_complexity = 0
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def __init__(self, tree, filename):
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self.tree = tree
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@classmethod
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def add_options(cls, parser):
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parser.add_option('--max-complexity', default=-1, action='store',
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type='int', help="McCabe complexity threshold")
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parser.config_options.append('max-complexity')
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@classmethod
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def parse_options(cls, options):
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cls.max_complexity = options.max_complexity
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def run(self):
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if self.max_complexity < 0:
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return
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visitor = PathGraphingAstVisitor()
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visitor.preorder(self.tree, visitor)
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for graph in visitor.graphs.values():
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if graph.complexity() >= self.max_complexity:
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text = self._error_tmpl % (graph.entity, graph.complexity())
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yield graph.lineno, 0, text, type(self)
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Since that is the defined entry point in the above ``setup.py``, flake8 finds
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it and uses it to register the extension.
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Existing Extensions
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===================
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This is not at all a comprehensive listing of existing extensions but simply a
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listing of the ones we are aware of:
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* `flake8-debugger <https://github.com/JBKahn/flake8-debugger>`_
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* `flake8-immediate <https://github.com/schlamar/flake8-immediate>`_
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* `flake8-print <https://github.com/JBKahn/flake8-print>`_
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* `flake8-todo <https://github.com/schlamar/flake8-todo>`_
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* `pep8-naming <https://github.com/flintwork/pep8-naming>`_
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* `radon <https://github.com/rubik/radon>`_
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* `flake8-import-order <https://github.com/public/flake8-import-order>`_
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* `flake8-respect-noqa <https://pypi.python.org/pypi/flake8-respect-noqa>`_
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.. links
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.. _mccabe: https://github.com/flintwork/mccabe
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.. _PyPI: https://pypi.python.org/pypi/ |