Make TLObjects picklable (#752)

telethon/tl/tlobject.py

@@ -5,12 +5,35 @@ from threading import Event
 
 class TLObject:
     def __init__(self):
-        self.confirm_received = Event()
         self.rpc_error = None
         self.result = None
 
         # These should be overrode
         self.content_related = False  # Only requests/functions/queries are
+        
+        # Internal parameter to tell pickler in which state Event object was
+        self._event_is_set = False 
+        self._set_event()
+
+    def _set_event(self):
+        self.confirm_received = Event()
+        
+        # Set Event state to 'set' if needed
+        if self._event_is_set:
+            self.confirm_received.set()
+
+    def __getstate__(self):
+        # Save state of the Event object 
+        self._event_is_set = self.confirm_received.is_set()
+        
+        # Exclude Event object from dict and return new state
+        new_dct = dict(self.__dict__)
+        del new_dct["confirm_received"]
+        return new_dct
+
+    def __setstate__(self, state):
+        self.__dict__ = state
+        self._set_event()
 
     # These should not be overrode
     @staticmethod