Model: Replace get_agents_of_type method with agents_by_type property

mesa/model.py

@@ -106,23 +106,16 @@ def agent_types(self) -> list[type]:
         """Return a list of all unique agent types registered with the model."""
         return list(self._agents_by_type.keys())
 
-    def agents_of_type(self, agenttype: type[Agent]) -> AgentSet:
-        """Retrieves an AgentSet containing all agents of the specified type.
-
-        Args:
-            agenttype: The type of agent to retrieve.
-
-        Raises:
-            KeyError: If agenttype does not exist
-
-
-        """
-        return self._agents_by_type[agenttype]
+    @property
+    def agents_by_type(self) -> dict[type[Agent], AgentSet]:
+        """A dictionary where the keys are agent types and the values are the corresponding AgentSets."""
+        return self._agents_by_type
 
     def get_agents_of_type(self, agenttype: type[Agent]) -> AgentSet:
         """Deprecated: Retrieves an AgentSet containing all agents of the specified type."""
         warnings.warn(
-            "get_agents_of_type is deprecated, please use agents_of_type instead.",
+            f"Model.get_agents_of_type() is deprecated, please replace get_agents_of_type({agenttype})"
+            f"with the property agents_by_type[{agenttype}].",
             DeprecationWarning,
             stacklevel=2,
         )