MYPYPATH directory used even if no __init__.py

[brandonchinn178]

Bug Report

According to the docs, when importing foo.bar, mypy will look through each directory in MYPYPATH and find a match. A directory is matched if it contains a __init__.py(i) file. However, I'm seeing behavior where an empty directory in MYPYPATH causes typechecking to fail.

To Reproduce

echo 'from foo.types import Foo' > main.py
mkdir -p foo/types/
echo 'Foo = 123' > foo/types/__init__.py
mkdir -p include/foo/types/

python3.13 -m venv venv
venv/bin/pip install mypy

# passes
rm -rf .mypy_cache && venv/bin/mypy main.py

# fails
rm -rf .mypy_cache && MYPYPATH=include venv/bin/mypy main.py

Expected Behavior

If <dir> does not contain any __init__.py files recursively, then adding MYPYPATH=<dir> should not make any difference

Actual Behavior

$ rm -rf .mypy_cache && venv/bin/mypy main.py
Success: no issues found in 1 source file

$ rm -rf .mypy_cache && MYPYPATH=include venv/bin/mypy main.py
main.py:1: error: Module "foo.types" has no attribute "Foo"  [attr-defined]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used:
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used:

[A5rocks]

Is this because namespace packages?

[brandonchinn178]

Yeah, possibly. In our actual codebase, we use --explicit-package-bases (we're using Bazel with Python, so we don't have explicit __init__.py files often).

From the docs:

The rules for searching for a module foo are as follows:

• The search looks in each of the directories in the search path (see above) until a match is found.
• If a package named foo is found (i.e. a directory foo containing an init.py or init.pyi file) that’s a match.
• If a stub file named foo.pyi is found, that’s a match.
• If a Python module named foo.py is found, that’s a match.

I don't see any mention of how namespace packages affect this; if they do, are these docs incomplete? It looks like namespace packages are only discussed in the section about specifying files on the command line.

[A5rocks]

I assume namespace package support was added after the documentation was added. If this issue is indeed because of namespace package support and also this is intended (I'm not sure, I haven't got much experience with it) then this should just be a documentation update.

[brandonchinn178]

You might be right; it looks like there's namespace logic in the module finder logic:

mypy/mypy/modulefinder.py

Line 563 in 3f50e3c

# In namespace mode, re-check those entries that had 'verify'.

Possibly just a docs update then