Pylance violating the Commutative Law with Union type ordering

Question

I have an interface specifying a position member. Because I want it to be agnostic to whether the member is implemented as a @property or a direct attribute, I annotate the type as a Union of the two

class Moveable(Protocol):
    position: property or Tuple[int, int]

entity: Moveable = Player() # Player implements `.position` as a getter

This works. However, switching the types around results in a Pylance error.

class Moveable(Protocol):
    position: Tuple[int, int] or property

(class) Player()
Expression of type "Player" cannot be assigned to declared type "Moveable"
  "Player" is incompatible with protocol "Moveable"
    "position" is invariant because it is mutable
    "position" is an incompatible type
      "property" is incompatible with "Tuple[int, int]"PylancereportGeneralTypeIssues

I’m not seeing why the order would matter, as (P or Q) <-> (Q or P). This violates the Commutative Law

Asked By: Michael Moreno

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Source

Answer 1

Instead of or, use Union[] or |

https://docs.python.org/3/library/typing.html#typing.Union

Answered By: ti7

Pylance violating the Commutative Law with Union type ordering

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