Incorrect argument substitution on Unpack[tuple[...]]

[JelleZijlstra]

Bug report

Bug description:

In the code below, all of the prints should be equivalent:

from typing import Generic, Tuple, TypeVarTuple, Unpack

Ts = TypeVarTuple("Ts")

class Old(Generic[*Ts]): ...
class New[*Ts]: ...

PartOld = Old[int, *Ts]
print(PartOld[str])
print(PartOld[*tuple[str]])
print(PartOld[*Tuple[str]])
print(PartOld[Unpack[tuple[str]]])  # Old[int, typing.Unpack[tuple[str]]]
print(PartOld[Unpack[Tuple[str]]])

PartNew = New[int, *Ts]
print(PartNew[str])
print(PartNew[*tuple[str]])
print(PartNew[*Tuple[str]])
print(PartNew[Unpack[tuple[str]]])  # New[int, typing.Unpack[tuple[str]]]
print(PartNew[Unpack[Tuple[str]]])

However, the Unpack[tuple[]] variants print something different. This is because the implementation of Unpack doesn't deal correctly with builtin aliases. I'll send a PR.

CPython versions tested on:

3.12, CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-118168: Fix Unpack interaction with builtin aliases #118169
• [3.12] gh-118168: Fix Unpack interaction with builtin aliases (GH-118169) #118178

[nineteendo]

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