Minor improvement to updates handling

Now the updates thread won't start unless you add,
at least, one updates handler. Also, if the TcpClient
was receiving (i.e., from an update), it will let the
update to be received first instead of crashing

tl/telegram_client.py

@@ -18,9 +18,6 @@ from tl.functions.help import GetConfigRequest
 from tl.functions.auth import SendCodeRequest, SignInRequest
 from tl.functions.messages import GetDialogsRequest, GetHistoryRequest, SendMessageRequest
 
-# For working with updates
-from tl.types import UpdateShortMessage
-
 
 class TelegramClient:
 
@@ -59,7 +56,6 @@ class TelegramClient:
                 self.session.save()
 
             self.sender = MtProtoSender(self.transport, self.session)
-            self.sender.add_update_handler(self.on_update)
 
             # Now it's time to send an InitConnectionRequest
             # This must always be invoked with the layer we'll be using
@@ -72,10 +68,6 @@ class TelegramClient:
 
             result = self.invoke(InvokeWithLayerRequest(layer=self.layer, query=query))
 
-            # Only listen for updates if we're authorized
-            if self.is_user_authorized():
-                self.sender.set_listen_for_updates(True)
-
             # We're only interested in the DC options,
             # although many other options are available!
             self.dc_options = result.dc_options
@@ -260,21 +252,18 @@ class TelegramClient:
                 return InputPeerChannel(channel.id, channel.access_hash)
 
         except StopIteration:
-            pass
-
-        return None
+            return None
 
     # endregion
 
     # region Updates handling
 
-    def on_update(self, tlobject):
-        """This method is fired when there are updates from Telegram.
-        Add your own implementation below, or simply override it!"""
+    def add_update_handler(self, handler):
+        """Adds an update handler (a function which takes a TLObject,
+          an update, as its parameter) and listens for updates"""
+        self.sender.add_update_handler(handler)
 
-        # Only show incoming messages
-        if type(tlobject) is UpdateShortMessage:
-            if not tlobject.out:
-                print('> User with ID {} said "{}"'.format(tlobject.user_id, tlobject.message))
+    def remove_update_handler(self, handler):
+        self.sender.remove_update_handler(handler)
 
     # endregion