"Yield value expected" on generator using send()

Bug Report

mypy doesn't allow empty yield statements in generator functions that accept send() values

To Reproduce

from typing import Any, Generator


def foo() -> Generator[int, Any, None]:
    yield
    while True:
        yield 42

Expected Behavior

I expected the second parameter (Any) in Generator[int, Any, None] to indicate that this generator accepts a send() value and that therefore the naked yield statement is accepting a value but not sending one. As far as I know the above code is idiomatic.

Actual Behavior

error: Yield value expected

mypy complains that a yield value is expected, but this standalone yield is for the purpose of accepting the value of a send() to the generator.

Your Environment

mypy 0.812
python 3.7

Inizia eseguendo l’esempio Python fornito con mypy e conferma la diagnostica “Yield value expected”. Traccia il modo in cui mypy verifica le istruzioni yield dei generatori e il tipo send di Generator; il lavoro è completato quando un yield senza espressione viene accettato in questo caso, con una copertura di regressione per l’esempio.