Exchanges: cleaner typing for subclass attributes

Author: carver

p2p/protocol.py

@@ -1,4 +1,4 @@
-from abc import ABC, abstractmethod
+from abc import ABC
 import logging
 import struct
 from typing import (
@@ -135,17 +135,14 @@ class BaseRequest(ABC, Generic[TRequestPayload]):
     Must define command_payload during init. This is the data that will
     be sent to the peer with the request command.
     """
+    # Defined at init time, with specific parameters:
     command_payload: TRequestPayload
 
-    @property
-    @abstractmethod
-    def cmd_type(self) -> Type[Command]:
-        raise NotImplementedError
-
-    @property
-    @abstractmethod
-    def response_type(self) -> Type[Command]:
-        raise NotImplementedError
+    # Defined as class attributes in subclasses
+    # outbound command type
+    cmd_type: Type[Command]
+    # response command type
+    response_type: Type[Command]
 
 
 class Protocol:

trinity/protocol/common/exchanges.py

@@ -41,6 +41,8 @@ class BaseExchange(ABC, Generic[TRequestPayload, TResponsePayload, TResult]):
     TResult is the response data after normalization
     """
 
+    request_class: Type[BaseRequest[TRequestPayload]]
+
     def __init__(self, mgr: ExchangeManager[TRequestPayload, TResponsePayload, TResult]) -> None:
         self._manager = mgr
 
@@ -72,15 +74,9 @@ async def get_result(
             timeout=timeout
         )
 
-    @property
-    @abstractmethod
-    def request_class(cls) -> Type[BaseRequest[TRequestPayload]]:
-        raise NotImplementedError('request_class must be defined on every Exchange')
-
     @classproperty
     def response_cmd_type(cls) -> Type[Command]:
-        # mypy is confused about the "abstract class property"
-        return cls.request_class.response_type  # type: ignore
+        return cls.request_class.response_type
 
     @abstractmethod
     async def __call__(self, *args: Any, **kwargs: Any) -> None: