ruff/docs/rules/implicit-namespace-package.md

implicit-namespace-package (INP001)

Derived from the flake8-no-pep420 linter.

What it does

Checks for packages that are missing an __init__.py file.

Why is this bad?

Python packages are directories that contain a file named __init__.py. The existence of this file indicates that the directory is a Python package, and so it can be imported the same way a module can be imported.

Directories that lack an __init__.py file can still be imported, but they're indicative of a special kind of package, known as a namespace package (see: PEP 420).

Namespace packages are a relatively new feature of Python, and they're not widely used. So a package that lacks an __init__.py file is typically meant to be a regular package, and the absence of the __init__.py file is probably an oversight.