Request: remove type constraints #492
Description
I'd like to create a PEP-484-style function annotation.
Like other annotations, my annotation:
- serves to document my code
- can be accessed at run-time via reflection (i.e. the inspect library).
- is irrelevant as far as the function itself is concerned
Let's call my annotation MoreThan, and say I can use it like so:
def make_booking(people : MoreThan[int, 5]) -> None:
assert isinstance(people, int), "Unexpected type"
assert people > 5, "Not enough people"
...
MoreThan is a very simple class:
class MoreThan:
def __init__(self, type_ : type = None, minimum : int = None):
self.type = type_
self.minimum = minimum
def __getitem__(self, item : Tuple[type, int]):
return MoreThan( item[0], item[1] )
And so all works hunky-dory, until I try to mix this with other PEP-484 annotations like:
def make_booking(people : Optional[MoreThan[int, 5]] = None) -> None:
...
This fails, because Optional/Union won't accept non-type parameters.
This can obviously be fixed by deriving MoreThan from type, or using my own version of Optional, but these add a big overhead, and feel like a bit of a hack considering MoreThan isn't actually instantiable.
It would be nice if the typing library either supported non-type derived annotations, or, if not possible, provided a simple mechanism for custom annotations.