I have another alternative idea. It will look like this:
let T = TypeVar("T") in
class list(Generic[T]):
def append(self, obj: T, /) -> None: ...
let T = TypeVar("T") in
let U = TypeVar("U") in
def two_tvars(x: T, y: U) -> T | U: ...
SimpleGenerator: TypeAlias = let T = TypeVar("T") in Generator[T, None, None]
def make_identity_func() -> let T = TypeVar("T") in Callable[[T], T]: ...
`let` would be a new soft keyword. The syntax would be available in all expressions and in class and def statements.
At runtime, the first example would be equivalent to something like:
T = TypeVar("T")
class list(Generic[T]):
def append(self, obj: T, /) -> None: ...
# allow runtime introspection of parameters
list.__set_parameters__({"T": T})
del T
Advantages:
* Less new syntax, so it is easier to get into the language and easier to extend with new flavors of type variables that we may introduce in the future.
* The new syntax is potentially useful outside of typing.
* Allows a way to explicitly scope type variables to part of a type or to a type alias.
Disadvantages:
* Less elegant syntax for generic classes (the flipside of it being more general).
* Does not remove the redundancy in T = TypeVar("T")