python / python/mypy

Return type of function overload is ignored if parameter has type Any

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bug topic-overloads
Dominant language
Python
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Description

Bug Report

mypy ignores the return type of a function if the annotation uses @overload and one of the parameters has type Any.

Possible duplicate of #14995.

To Reproduce
https://mypy-play.net/?mypy=1.1.1&python=3.11&gist=5ca80f2b256e4d31a8c588b15702b085

@overload
def toInt(value: int) -> int: ...

@overload
def toInt(value: float) -> int: ...

@overload
def toInt(value: Any) -> int | None: ...

def toInt(value: Any) -> int | None:
    try:
        return int(value)
    except (TypeError, ValueError):
        return None


reveal_type(toInt(1))
any_obj: Any = object()
reveal_type(toInt(any_obj))

Expected Behavior

Revealed type is "builtins.int"
Revealed type is "Union[builtins.int, None]"

Actual Behavior
Output of mypy

Revealed type is "builtins.int"
Revealed type is "Any"

vs. output of pyright

Type of "toInt(1)" is "int"
Type of "toInt(any_obj)" is "int | None"

Your Environment

  • Mypy version used: 1.1.1
  • Mypy command-line flags: --python-version 3.11
  • Mypy configuration options from mypy.ini (and other config files): None
  • Python version used: 3.11.2

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked mypy-play reproduction using mypy 1.1.1 and Python 3.11, then inspect overload resolution for calls whose argument is typed as Any. The fix is done when reveal_type reports int for the int call and int | None for the Any call, matching the expected output and pyright comparison.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
devtools
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
30/100

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