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Doc review: extensions
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Writing an Extension for Flake8
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Writing an Extension for Flake8
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===============================
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===============================
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Since Flake8 is now adding support for extensions, we require ``setuptools``
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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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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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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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``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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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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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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then this would look something like the following::
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@ -18,57 +18,38 @@ then this would look something like the following::
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# ...
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# ...
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)
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)
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We used ``P10`` here, but in reality, you should check to prevent as much
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future overlap as possible with other extensions. ``W`` and ``E`` followed by
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three digits should be considered entirely reserved for pep8. ``F`` should be
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considered reserved for Pyflakes and ``C`` for McCabe. Also, in anticipation
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of possible pylint integration, ``W`` and ``E`` followed by four digits should
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be considered reserved. We have no way of checking for those though, so while
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we ask you not use them, we can not (currently) prevent you from doing so.
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A Real Example: McCabe
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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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----------------------
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Below is an example from mccabe_ for how to write your ``setup.py`` file for
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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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your Flake8 extension.
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.. code-block:: python
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.. code-block:: python
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# https://github.com/florentx/mccabe/blob/master/setup.py
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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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# -*- coding: utf-8 -*-
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from __future__ import with_statement
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from setuptools import setup
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from setuptools import setup
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# ...
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def get_version(fname='mccabe.py'):
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with open(fname) as f:
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for line in f:
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if line.startswith('__version__'):
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return eval(line.split('=')[-1])
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def get_long_description():
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descr = []
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for fname in ('README.rst',):
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with open(fname) as f:
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descr.append(f.read())
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return '\n\n'.join(descr)
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setup(
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setup(
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name='mccabe',
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name='mccabe',
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version=get_version(),
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description="McCabe checker, plugin for flake8",
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# ...
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long_description=get_long_description(),
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keywords='flake8 mccabe',
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author='Tarek Ziade',
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author_email='tarek@ziade.org',
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maintainer='Florent Xicluna',
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maintainer_email='florent.xicluna@gmail.com',
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url='https://github.com/florentx/mccabe',
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license='Expat license',
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py_modules=['mccabe'],
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zip_safe=False,
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install_requires=[
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install_requires=[
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'setuptools',
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'setuptools',
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],
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],
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@ -77,26 +58,17 @@ your Flake8 extension.
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'C90 = mccabe:McCabeChecker',
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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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classifiers=[
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'Development Status :: 3 - Alpha',
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# ...
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'Environment :: Console',
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'Intended Audience :: Developers',
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'License :: OSI Approved :: MIT License',
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'Operating System :: OS Independent',
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'Programming Language :: Python',
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'Programming Language :: Python :: 2',
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'Programming Language :: Python :: 3',
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'Topic :: Software Development :: Libraries :: Python Modules',
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'Topic :: Software Development :: Quality Assurance',
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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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In ``mccabe.py`` you can see that extra options are added to the parser when
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flake8 registers the extensions:
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flake8 registers the extension:
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.. code-block:: python
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.. code-block:: python
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# https://github.com/florentx/mccabe/blob/e88be51e0c6c2bd1b87d7a44b7e71b78fdc53959/mccabe.py#L225
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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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class McCabeChecker(object):
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"""McCabe cyclomatic complexity checker."""
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"""McCabe cyclomatic complexity checker."""
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name = 'mccabe'
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name = 'mccabe'
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@ -128,9 +100,10 @@ flake8 registers the extensions:
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text = self._error_tmpl % (graph.entity, graph.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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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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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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it and uses it to register the extension.
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.. links
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.. links
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.. _mccabe: https://github.com/florentx/mccabe
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.. _mccabe: https://github.com/flintwork/mccabe
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.. _PyPI: https://pypi.python.org/pypi/
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.. _PyPI: https://pypi.python.org/pypi/
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