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https://github.com/adamchainz/flake8-no-pep420

A flake8 plugin to ban PEP-420 implicit namespace packages.
https://github.com/adamchainz/flake8-no-pep420

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A flake8 plugin to ban PEP-420 implicit namespace packages.

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flake8-no-pep420

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A `flake8 `_ plugin to ban `PEP-420 `__ implicit namespace packages.



----



**Linting a Django project?**

Check out my book `Boost Your Django DX `__ which covers Flake8 and many other code quality tools.



----



Requirements

============



Python 3.8 to 3.12 supported.



Installation

============



First, install with ``pip``:



.. code-block:: sh



     python -m pip install flake8-no-pep420



Second, if you define Flake8’s ``select`` setting, add the ``INP`` prefix to it.

Otherwise, the plugin should be active by default.



Rationale

=========



Implicit namespace packages are directories of Python files without an ``__init__.py``.

They’re valid and importable, but they break some tools:



* unittest test discovery, unless |-s (--start-directory)|__ points to the namespace package.

  By extension, this affects Django’s test runner too.



  .. |-s (--start-directory)| replace:: ``-s`` (``--start-directory``)

  __ https://docs.python.org/3/library/unittest.html#cmdoption-unittest-discover-s



* Coverage.py, unless |report.include_namespace_packages|__ is enabled.



  .. |report.include_namespace_packages| replace:: ``report.include_namespace_packages``

  __ https://coverage.readthedocs.io/en/latest/config.html#report-include-namespace-packages



* pytest (`Issue #5147 `__)



In most cases, tools fail silently, which can lead to a false sense of security:



* Tests may look legitimate but never run

* Code may be untested but not appear in coverage statistics



PEP-420’s algorithm is non-trivial which is probably why such tools haven’t (yet) implemented it.



Rules

=====



INP001: File is part of an implicit namespace package. Add __init__.py?

-----------------------------------------------------------------------



flake8-no-pep420 will trigger this on the first line of any file that sits in a directory without an ``__init__.py`` file.



Often projects have a few root files *not* in packages, for which an ``__init__.py`` file should not be added.

For example, Django projects normally have a ``manage.py`` file in the root of their repository.

In these cases you can ignore the ``INP001`` error.

It’s possible to use ``# noqa: INP001`` to ignore the error in-line, but this isn’t possible if the first line is a `shebang `__, such as in Django’s ``manage.py``.

In such cases it’s preferable to use Flake8’s `per-file-ignores option `__, for example in ``setup.cfg``:



.. code-block:: ini



    [flake8]

    # ...

    per-file-ignores =

        manage.py:INP001