Bug report

Bug description:

The following statement is invalid:

type X[T_default=int, T] = (T_default, U) 
# SyntaxError: non-default type parameter 'T' follows default type parameter

However, writing it as a TypeAliasType is possible. The following should likely raise an error as well to mimic this behavior:

from typing import TypeAliasType, TypeVar
T = TypeVar('T')
T_default = TypeVar("T_default", default=int)
TypeAliasType("TupleT_default_reversed", tuple[T_default, T], type_params=(T_default, T))
print("OK")

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-124787: Fix TypeAliasType and incorrect type_params #124795