Always complain if returning a value if annotated to return None

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#1,509 3 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
compilers, devtools

Research direction

Start by reproducing the issue's two-function example and trace how mypy analyzes a return statement in a function annotated to return None when the returned expression has type Any. Done means mypy reports this return as an error while preserving the intended handling of valid None returns.

Written by the indexing model from the issue text.

Description

priority-1-normal topic-strict-optional

Mypy doesn't complain about this code that returns a value in a function declared to return None, since the return value is Any:

def f() -> None:
    return g()   # oops, but no error

def g():
    return 1

I think that mypy could complain about the return statement even if the value has type Any. The current behavior is not inconsistent or incorrect, but probably not optimal.

Dominant language
Python
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