A flake8 plugin to ban PEP-420 implicit namespace packages.
Python 3.6 to 3.10 supported.
First, install with pip:
python -m pip install flake8-no-pep420
Second, check that flake8 lists the plugin in its version line:
$ flake8 --version 3.8.4 (flake8-no-pep420: 1.0.0, mccabe: 0.6.1, pycodestyle: 2.5.0, pyflakes: 2.1.1) CPython 3.8.0 on Darwin
Third, add the INP prefix to your select list. For example, if you have your configuration in setup.cfg:
[flake8] select = E,F,W,INP
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Implicit namespace packages are directories of Python files without an __init__.py. They’re valid and importable, but unfortunately they’re silently ignored by many tools, like:
- unittest test discovery (and by extension, Django’s test runner)
- Mypy without its –namespace-packages option
Such silent failure leads to a false sense of security:
- Tests may look legitimate but never run
- Code may be untested but not affect coverage statistics
- Types may never be checked
PEP-420’s algorithm is non-trivial which is probably why such tools haven’t (yet) implemented it.
INP001: File is part of an implicit namespace package.
flake8-no-pep420 will trigger this on the first line of any file that sits in a directory without a __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. As such, it’s preferable to use Flake8’s per-file-ignores option, for example in setup.cfg:
[flake8] # ... per-file-ignores = manage.py:INP001
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