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Making functions/methods subscriptable

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python

Research direction

Start by reading the linked python-ideas discussion, then review PEP 612 and issue #946 to understand the stated limitations. The proposal involves subscriptable FunctionType and related types, descriptor binding, and likely type-checker special cases; done would require an agreed design and corresponding type-checker support.

Written by the indexing model from the issue text.

Description

topic: feature

I'd like to make both instances and the types of functions and methods (including builtin methods) subscriptable.

Part of this proposal has been discussed already on python-ideas (https://discuss.python.org/t/making-functions-subscriptable-at-runtime/26463) but I thought it might also be worthwhile making FunctionType etc. subscriptable and work in a similar way to Callable just with extra descriptor behaviour that binds it into a MethodType.

class Foo:
	bar: FunctionType[[Self, int], str]
	# equivalent to 
	def bar(self, arg1, /) -> str: ...

This is different from Callable as if FunctionType was replaced with Callable, bar would always require a self argument.

This unfortunately probably requires special casing in type checkers as it isn't quite currently possible with PEP 612 (ParamSpec + Concatenate) (see #946) unless the PEP is updated

Dominant language
Python
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Avg merge
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Merged PRs (30d)
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