Implement __str__ for History

parlai/core/torch_agent.py

@@ -295,7 +295,7 @@ def update_history(self, obs: Message, temp_history: Optional[str] = None):
 
         self.temp_history = temp_history
 
-    def get_history_str(self):
+    def get_history_str(self) -> Optional[str]:
         """
         Return the string version of the history.
         """
@@ -346,6 +346,9 @@ def _add_person_tokens(self, text, token, add_after_newln=False):
         else:
             return token + ' ' + text
 
+    def __str__(self) -> str:
+        return self.get_history_str() or ''
+
 
 class TorchAgent(ABC, Agent):
     """