Added StopPropagation logic

readthedocs/extra/basic/working-with-updates.rst

@@ -121,11 +121,35 @@ random number, while if you say ``'eval 4+4'``, you will reply with the
 solution. Try it!
 
 
+Stopping propagation of Updates
+*******************************
+
+There might be cases when an event handler is supposed to be used solitary and
+it makes no sense to process any other handlers in the chain. For this case,
+it is possible to raise a ``StopPropagation`` exception which will cause the
+propagation of the update through your handlers to stop:
+
+    .. code-block:: python
+
+        @client.on(events.NewMessage)
+        def _(event):
+            # ... some conditions
+            event.delete()
+
+            # Other handlers won't have an event to work with
+            raise client.StopPropagation
+
+        @client.on(events.NewMessage)
+        def _(event):
+            pass  # Will never be reached, because
+                  # it is the second handler in the chain.
+
+
 Events module
 *************
 
 .. automodule:: telethon.events
-    :members:
+:members:
         :undoc-members:
         :show-inheritance:
 

telethon/telegram_client.py

@@ -15,9 +15,7 @@ from mimetypes import guess_type
 
 from .crypto import CdnDecrypter
 from .tl.custom import InputSizedFile
-from .tl.functions.upload import (
-    SaveBigFilePartRequest, SaveFilePartRequest, GetFileRequest
-)
+from .tl.functions.upload import (GetFileRequest, SaveBigFilePartRequest, SaveFilePartRequest)
 from .tl.types.upload import FileCdnRedirect
 
 try:
@@ -1768,6 +1766,7 @@ class TelegramClient(TelegramBareClient):
                 The event builder class or instance to be used,
                 for instance ``events.NewMessage``.
         """
+
         def decorator(f):
             self.add_event_handler(f, event)
             return f
@@ -1779,7 +1778,13 @@ class TelegramClient(TelegramBareClient):
             event = builder.build(update)
             if event:
                 event._client = self
+                try:
                     callback(event)
+                except StopPropagation:
+                    __log__.info("Event handler {0} stopped propagation of updates while processing {1}.".format(
+                        callback.__name__,
+                        update))
+                    break
 
     def add_event_handler(self, callback, event):
         """
@@ -2014,3 +2019,30 @@ class TelegramClient(TelegramBareClient):
         )
 
     # endregion
+
+
+# region Exceptions
+
+class StopPropagation(Exception):
+    """
+    If this Exception is found to be raised in any of the handlers for a
+    given update, it will stop the execution of all other registered
+    event handlers in the chain.
+    Think of it like a ``StopIteration`` exception in a for loop.
+
+    Example usage:
+    ```
+    @client.on(events.NewMessage)
+    def delete(event):
+        event.delete()
+        # Other handlers won't have an event to work with
+        raise StopPropagation
+
+    @client.on(events.NewMessage)
+    def _(event):
+        pass  # Will never be reached, because
+              # it is the second handler in the chain.
+    ```
+    """
+
+# endregion