On: Python 3 Types in the Wild: A Tale of Two Type Sys...

[codethief]

Besides, there is a difference between the actual type of the objects `a` and `b` in `a == b` and the structural type you specify in an annotation.

For instance:

  from typing import Protocol


  class MyClass:
      def method_a(self) -> None:
          ...

      def method_b(self) -> None:
          ...


  class ProtocolA(Protocol):
      def method_a(self) -> None:
          ...


  class ProtocolB(Protocol):
      def method_b(self) -> None:
          ...


  def compare(a: ProtocolA, b: ProtocolB):
      if a == b:
          print("a == b")
      else:
          print("a != b")


  a = MyClass()
  b = MyClass()

  compare(a, b)

Clearly, you would expect the output to be "a == b".