use explicit Optional[...] for parameters with None as a default in datastructures.py

[adriangb]

See https://www.python.org/dev/peps/pep-0484/#union-types

[Kludex]

See https://www.python.org/dev/peps/pep-0484/#id29

The link is "not found".

[adriangb]

Weird, it got mangled, it should be https://www.python.org/dev/peps/pep-0484/#union-types

[adriangb]

Specifically:

A past version of this PEP allowed type checkers to assume an optional type when the default value is None, as in this code:

def handle_employee(e: Employee = None): ...

This would have been treated as equivalent to:

def handle_employee(e: Optional[Employee] = None) -> None: ...

This is no longer the recommended behavior. Type checkers should move towards requiring the optional type to be made explicit.

[tomchristie]

Sure. Don't know what the motivation is behind...

This is no longer the recommended behavior. Type checkers should move towards requiring the optional type to be made explicit.

But happy enough either ways. 😌

[adriangb]

There's probably discussions on the topic in BPO and such. Personally my motivation is just to make sure the project works as well as possible with type checkers.