Bug report

Bug description:

We disallow certain expressions (e.g., yield) in type parameters bounds, constraints, and defaults. But the error message always says it's a bound:

>>> def f[T=(yield)](): pass
  File "<python-input-0>", line 1
SyntaxError: yield expression cannot be used within a TypeVar bound

>>> def f[T: (int, (yield))](): pass
  File "<python-input-2>", line 1
SyntaxError: yield expression cannot be used within a TypeVar bound

We could either add some machinery in the symbol table so it knows whether we're in a bound, constraints, or default, or just change the error message to something like "within a TypeVar bound, constraints, or default".

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-119933 : Improve SyntaxError message for invalid type parameters expressions #119976
• [3.13] gh-119933: Improve SyntaxError message for invalid type parameters expressions (GH-119976) #120641