Hi everyone 👋 I’m trying to incorporate

mypy

as a pants check goal, but I’m having some trouble, specifically with 3rd party plugins. My

mypy.ini

file (see snippet below) declares plugins for pydantic and strawberry, both of which are defined in poetry in my pyproject.toml.

[mypy]
plugins = pydantic.mypy, strawberry.ext.mypy_plugin

The problem I’m running into is that mypy can’t import the plugin, despite having run

pants generate-lockfile

recently with the most up-to-date dependencies.

mypy.ini:8:1: error: Error importing plugin "pydantic.mypy": No module named 'pydantic'  [misc]
    plugins = pydantic.mypy, strawberry.ext.mypy_plugin

I tried looking through past threads to understand what needs to be done to support 3rd party libraries with mypy, but I’m getting a bit lost.

Sorry for the trouble. Can you share your pants.toml file?

Hard to debug without the pants.toml - but I've used something like this in the past (fastapi on Pants 2.17):

[mypy]
lockfile = "build-support/python/mypy.lock"
version = "mypy==1.2.0"
extra_requirements = ["pydantic"]

mypy.ini

[mypy]
plugins = pydantic.mypy

Of course!

[GLOBAL]
pants_version = "2.20.0"
colors = true

# Packages needed for pants to run various goals
backend_packages = [
  "pants.backend.python",
  "pants.backend.experimental.python.lint.ruff.check",
  "pants.backend.experimental.python.lint.ruff.format",
  "pants.backend.python.typecheck.mypy",
]

[anonymous-telemetry]
enabled = true
repo_id = "88035b17-7ce9-48d2-a168-4d5d20095e4e"

[source]
# Directory structure rooted around a shared modules directory and various services
root_patterns = [
  "/shared",
  "/services",
  "/cron_jobs",
  "/tests",
  "/scripts",
  "/docker/localstack"
]

[python]
# The default interpreter constraints for code in this repo. Individual targets can override
#  this with the `interpreter_constraints` field. See
#  <https://www.pantsbuild.org/docs/python-interpreter-compatibility>.

# Modify this if you don't have Python 3.9 on your machine.
# This can be a range, such as [">=3.8,<3.11"], but it's usually recommended to restrict
# to a single minor version.
interpreter_constraints = ["CPython==3.10.*"]

# Enable the "resolves" mechanism, which turns on lockfiles for user code. See
# <https://www.pantsbuild.org/docs/python-third-party-dependencies>. This also adds the
# `generate-lockfiles` goal for Pants to generate the lockfile for you.
enable_resolves = true

[python.resolves]
python-default = "lockfiles/python-default.lock"

[python-bootstrap]
# We search for interpreters both on the $PATH and in the `$(pyenv root)/versions` folder.
# If you're using macOS, you may want to leave off the <PATH> entry to avoid using the
# problematic system Pythons. See
# <https://www.pantsbuild.org/docs/python-interpreter-compatibility#changing-the-interpreter-search-path>.

search_path = ["<PYENV_LOCAL>"]

[ruff]
config = "ruff.toml"

[mypy]
config = "mypy.ini"
args = ["--show-error-codes", "--pretty", "--show-column-numbers"]
requirements = [
  "pydantic>=2.6.3",
  "sqlalchemy>=2.0.0",
  "strawberry-graphql>=0.217.0",
]

Can you provide a rough folder layout of what you're trying to typecheck against where the

mypy.ini

is? I've upgraded my project to 2.20, it seems to still work, but when I put a mypy.ini in the "wrong" place, then everything blew up and I got the same pydantic error

My

mypy.ini

file is at the root of my project. I then have most of my code in the top-level shared and services packages.

Yeah, that's what I just tested and it fails - whereas when I have my mypy.ini files in the source roots, it seems to work... That's interesting to note

Oh interesting, so for your project, there’s a single root package, and you have the mypy.ini within that?

Its a monorepo, so per sub-project I had a separate mypy.ini - i havent looked at that project in a while, so I'll need to look at it again tonight to make sure its doing what I think

I haven’t yet tried the

install_from_resolve

configuration, let me give that a shot

Okay, no idea if it'll work - but in my projects, I split up the tooling and tooling deps from the production. Just a force of habit maybe

I think that did the trick! Just to tie up loose ends, any idea why this fix worked?

The docs need some tweaks, but generally they're explained here: https://www.pantsbuild.org/2.20/reference/subsystems/mypy#install_from_resolve The "tool" (mypy) needs to be installed with the resolve