[New-bugs-announce] [issue46821] Introspection support for typing.overload

Jelle Zijlstra report at bugs.python.org
Mon Feb 21 14:58:17 EST 2022

New submission from Jelle Zijlstra <jelle.zijlstra at gmail.com>:

Currently, the implementation of @overload (https://github.com/python/cpython/blob/59585d6b2ea50d7bc3a9b336da5bde61367f527c/Lib/typing.py#L2211) simply returns a dummy function and throws away the decorated function. This makes it virtually impossible for type checkers using the runtime function object to find overloads specified at runtime.

In pyanalyze, I worked around this by providing a custom @overload decorator, working something like this:

_overloads: dict[str, list[Callable]] = {}

def _get_key(func: Callable) -> str:
    return f"{func.__module__}.{func.__qualname__}"

def overload(func):
    key = _get_key(func)
    _overloads.setdefault(key, []).append(func)
    return _overload_dummy

def get_overloads_for(func):
    key = _get_key(func)
    return _overloads.get(key, [])

A full implementation will need more error handling.

I'd like to add something like this to typing.py so that other tools can also use this information.

assignee: Jelle Zijlstra
components: Library (Lib)
messages: 413671
nosy: AlexWaygood, Jelle Zijlstra, gvanrossum, kj, sobolevn
priority: normal
severity: normal
status: open
title: Introspection support for typing.overload
type: enhancement
versions: Python 3.11

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