Not reporting any error when function returns bool type while expecting str type

Hi

I noticed a situation where I wasn't getting a type error from mypy when I would have expected to get one.

Below is the code I have. I purposefully set the return type to str because I wanted to see a mypy error, and specifically I expected the error to be that I had set the wrong return type (e.g. as the code is doing a comparison, which will thus return a bool type, I expected mypy to say the return type should be of type bool):

def is_dev() -> str:
    return settings.get("environment") == "dev"

In that code snippet you'll see settings.get(...), which is a function that returns a string, and we compare that string against another string.

Note: as settings.get is custom code, mypy knows nothing about what type is being returned.

My hypothesis is that because my specific example uses code that mypy can't identify the type for (i.e. settings.get()), mypy just goes ahead and ignores any other possible type check errors (such as me specifying the return type as str).

If that's expected of mypy then fine, but it just confused me.

I'm using mypy version 0.782 and Python version 3.7.7.

I'm running mypy in two places:

1. vim integration (e.g. mypy --ignore-missing-imports --strict-equality)
2. tox (e.g. mypy --ignore-missing-imports --package foo)

Note: I've tried also changing to --no-strict-equality and it makes no difference.

Thank you for any guidance you can give me.

Reproduziere die gemeldete Funktion mit mypy 0.782, Python 3.7.7 und den aufgeführten Optionen --strict-equality und --ignore-missing-imports und vergleiche anschließend die Diagnosen mit dem erwarteten Fehler für den Rückgabetyp. Verfolge den Typprüfpfad für Rückgabeausdrücke und unbekannte Typen; als erledigt gilt die Aufgabe, wenn das Verhalten korrigiert oder eindeutig mit einem Regressionstest dokumentiert ist.