flake8-no-pep420
A flake8 plugin to ban PEP-420 implicit namespace packages.
Requirements
Python 3.8 to 3.12 supported.
Installation
First, install with pip
:
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.
Linting a Django project? Check out my book Boost Your Django DX which covers Flake8 and many other code quality tools.
Rationale
Implicit namespace packages are directories of Python files without an __init__.py
.
They’re valid and importable, but they break many tools, such as:
- unittest test discovery (and by extension, Django’s test runner)
- Coverage.py
- Mypy without its --namespace-packages option
- pytest
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
- Types may never be checked
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
:
[flake8]
# ...
per-file-ignores =
manage.py:INP001