Reflex Mypy Example

This is a minimal example to show how normal, by-the-docs Reflex code causes Mypy to fail. It's linked to Issue 3374 in the Reflex repo.

How to reproduce

1. Clone this repository

git clone [email protected]:etjones-erisyon/reflex_mypy_example.git

2. Create & activate a virtual environment

python3 -m venv venv; source ./venv/bin/activate

3. Install the requirements

pip install -r requirements.txt

4. Init Reflex

reflex init

5. Confirm Reflex is running as intended.

reflex run

(And load page at http://localhost:3000 to see the Reflex app running) 6. Run Mypy

mypy .

7. Observe the error Mypy flags

(venv) [ reflex_mypy  $] mypy .
rxconfig.py:1: error: Skipping analyzing "reflex": module is installed, but missing library stubs or py.typed marker  [import-untyped]
reflex_mypy/reflex_mypy.py:1: error: Skipping analyzing "reflex": module is installed, but missing library stubs or py.typed marker  [import-untyped]
reflex_mypy/reflex_mypy.py:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
reflex_mypy/reflex_mypy.py:24: error: Missing positional argument "arg" in call to "increment_by" of "State"  [call-arg]
reflex_mypy/reflex_mypy.py:24: error: Argument 1 to "increment_by" of "State" has incompatible type "int"; expected "State"  [arg-type]

The usage on line 24 of reflex_mypy.py is as follows:

rx.button(State.counter_message, on_click=lambda: State.increment_by(1)),

This breaks normal Python expectations, where we would usually either expect the State.increment_by() to be decorated as a @staticmethod or @classmethod or to be called on an instance of State rather than the class itself. Reflex doesn't do this, so Mypy flags it as an error.