ConversationHandler: Docs & edited_channel_post behavior (#2339)

* Update docs & ignore edited channel posts

* typo

* Apply suggestions from code review

Co-authored-by: Poolitzer <25934244+Poolitzer@users.noreply.github.com>

* Update telegram/ext/conversationhandler.py

* fix pre-commit

Co-authored-by: Poolitzer <25934244+Poolitzer@users.noreply.github.com>

telegram/ext/conversationhandler.py

@@ -58,8 +58,22 @@ class _ConversationTimeoutContext:
 
 class ConversationHandler(Handler[Update]):
     """
-    A handler to hold a conversation with a single user by managing four collections of other
-    handlers.
+    A handler to hold a conversation with a single or multiple users through Telegram updates by
+    managing four collections of other handlers.
+
+    Note:
+        ``ConversationHandler`` will only accept updates that are (subclass-)instances of
+        :class:`telegram.Update`. This is, because depending on the :attr:`per_user` and
+        :attr:`per_chat` ``ConversationHandler`` relies on
+        :attr:`telegram.Update.effective_user` and/or :attr:`telegram.Update.effective_chat` in
+        order to determine which conversation an update should belong to. For ``per_message=True``,
+        ``ConversationHandler`` uses ``update.callback_query.message.message_id`` when
+        ``per_chat=True`` and ``update.callback_query.inline_message_id`` when ``per_chat=False``.
+        For a more detailed explanation, please see our `FAQ`_.
+
+        Finally, ``ConversationHandler``, does *not* handle (edited) channel posts.
+
+    .. _`FAQ`: https://git.io/JtcyU
 
     The first collection, a ``list`` named :attr:`entry_points`, is used to initiate the
     conversation, for example with a :class:`telegram.ext.CommandHandler` or
@@ -424,7 +438,7 @@ class ConversationHandler(Handler[Update]):
         if not isinstance(update, Update):
             return None
         # Ignore messages in channels
-        if update.channel_post:
+        if update.channel_post or update.edited_channel_post:
             return None
         if self.per_chat and not update.effective_chat:
             return None

tests/test_conversationhandler.py

@@ -726,10 +726,14 @@ class TestConversationHandler:
 
     def test_channel_message_without_chat(self, bot):
         handler = ConversationHandler(
-            entry_points=[CommandHandler('start', self.start_end)], states={}, fallbacks=[]
+            entry_points=[MessageHandler(Filters.all, self.start_end)], states={}, fallbacks=[]
         )
-        message = Message(0, None, None, Chat(0, Chat.CHANNEL, 'Misses Test'), bot=bot)
-        update = Update(0, message=message)
+        message = Message(0, date=None, chat=Chat(0, Chat.CHANNEL, 'Misses Test'), bot=bot)
+
+        update = Update(0, channel_post=message)
+        assert not handler.check_update(update)
+
+        update = Update(0, edited_channel_post=message)
         assert not handler.check_update(update)
 
     def test_all_update_types(self, dp, bot, user1):