Hey experts, I’m trying to get mypy running in my pants workspace, but for some reason running

./pants check path/to/dir

just gives me

error: Cannot find implementation or library stub for module named

errors for all my imports. Running the actual

./pants run

seems to work just fine. Do I need to setup mypy somehow to correctly understand the structure of my pants workspace? For example explicitly putting the root or something in the options?

Not sure without more information about the structure of your repo (e.g. do you have namespace packages? whats your mypy config?) I ran into this with the pants repo proper, but this might point out some ideas? https://sureshjoshi.com/development/pants-plugin-code-quality#typechecking

I did see that blog actually, and I indeed don’t have init files: The problem tends to be a missing

__init__.py

Pants tries/tends not to impose its will on your code.

mypy

can do whatever it want, however. So, if it's complaining about something, it's probably init or config (using namespace packages, for example). You can try it out by manually pip installing the same mypy version you're using in pants, and running directly. It should give you a similar result

I guess I’m not fully familiar with how Pants sets up the structure under the hood — I know Pants doesn’t require init files when executing, nor the standard package layout that a typical Python package might use by default. I’d assumed mypy in Pants would automatically be configured to use the structure of my pants repo, but it sounds like that’s not true?

Creating a /src/project/__init_ .py works

hmmm I see, so for a larger project does this mean I must explicitly have init files for all my subdirectories? Do you know if there’s a way to specify to either mypy or pants that the tool should be run with whatever magic pants uses to not have those init files?

So, if you install

mypy

directly and run

mypy .

- you get the same error.

(.venv) ⏺ scratch/pants-mypy-test % mypy .                                                                                                                                                               ⎇ main*
src/project/main.py:1: error: Cannot find implementation or library stub for module named "project.lib"  [import]
src/project/main.py:1: note: See <https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports>

In this situation, Pants is just passing through the error it gets from the underlying tools. if you run

./pants check :: --keep-sandboxes=always

you can hop into exactly what's being run in the

__run.sh

script

Got it, yeah adding the init files does seem to fix it, just wondering if there’s a way to avoid having to restructure the whole repo. Thanks for your help!

I -think- you're going to want to look at implicit vs explicit namespace stuff in mypy (or the associated PEP). I'll be the first to say I don't understand much of that, since that's not typically how I structure my repos. https://peps.python.org/pep-0420/ https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-no-namespace-packages https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-explicit-package-bases