Add the Chat.creator dynamic attribute

This new attribute returns the original creator of the group chat,
fetching it from a new API introduced in the Bot API 2.1 update.

Issue: GH-64

Author: Pietro Albini

botogram/objects/chats.py

@@ -144,6 +144,27 @@ def admins(self):
         # returned as a list (the tuple thing is an implementation detail)
         return list(self._cache_admins)
 
+    @property
+    def creator(self):
+        """Get the creator of this chat"""
+        # If this is a private chat, return the current user since Telegram
+        # doesn't support `getChatAdministrators` for private chats
+        if self.type == "private":
+            return self._to_user()
+        elif self.type == "channel":
+            raise TypeError("Not available on channels")
+
+        # Be sure to cache the chat creator
+        if not hasattr(self, "_cache_creator"):
+            # Get a list of the admins and fetch only the creator
+            members = self._api.call("getChatAdministrators",
+                                     {"chat_id": self.id},
+                                     expect=multiple(ChatMember))
+            self._cache_creator = [member.user for member in members
+                                   if member.status == "creator"][0]
+
+        return self._cache_creator
+
     def leave(self):
         """Leave this chat"""
         if self.type not in ("group", "supergroup"):

docs/api/telegram.rst

@@ -407,6 +407,33 @@ about its business.
 
       .. versionadded:: 0.3
 
+   .. py:attribute:: creator
+
+      Return the creator of the group (or supergroup), represented as an
+      :py:class:`~botogram.User`. If the chat is a private chat, the chat
+      partner is returned. Instead, a ``TypeError`` is raised if the chat is a
+      channel.
+
+      Please remember the content of this attribute is fetched from Telegram
+      the first time you access it (so it might be slow), but it's cached right
+      after, so the following accesses will involve no network communication.
+
+      .. code-block:: python
+         :emphasize-lines: 4,5,6
+
+         @bot.command("antiflood_limit")
+         def antiflood_limit_command(shared, chat, message, args):
+             """Set the antiflood limit"""
+             # Only the chat creator should be able to do this
+             if message.sender != chat.creator:
+                 message.reply("You're not the creator of the chat")
+
+             if len(args) != 1:
+                 message.reply("You need to provide just the new limit!")
+             shared["antiflood_limit"] = int(args[0])
+
+      .. versionadded:: 0.3
+
    .. py:method:: leave()
 
       Kick the bot from this chat. This method is available only on groups and

docs/changelog.rst

@@ -48,6 +48,7 @@ New features
 * Added new attribute :py:attr:`botogram.Message.pinned_message`
 * Added new attribute :py:attr:`botogram.Sticker.emoji`
 * Added new attribute :py:attr:`botogram.Chat.admins`
+* Added new attribute :py:attr:`botogram.Chat.creator`
 * Added new method :py:meth:`botogram.Chat.leave`
 * Every method which sends something to a chat now returns the sent
   :py:class:`~botogram.Message`