Walrus in comprehension can leak into PEP 695 scope

[JelleZijlstra]

Example:

>>> class B: pass
... 
>>> class X[T]([(x := 3) for _ in range(2)] and B): print(x)
... 
3

This is because a walrus in a comprehension assigns to the immediately enclosing scope, which is now the type parameter scope. I don't think this causes any concrete problem right now, but I don't like it because I'd like to preserve the invariant that type parameters are the only names that can be defined in PEP 695 scopes.

Linked PRs

• gh-104640: Disallow walrus in comprehension within type scopes #104641