Add new event system

Add event system based on a public dispatch method in Client.  The new
event system bases itself on two types of events, internal event
handlers and user defined event handlers.  Internal event handlers begin
with 'handle_', and user defined events begin with 'on_'.  Events are
dispatched with dispatch(event_name, *args).  The Client class should be
subclassed and the on_<event> handlers defined in it for responding to
events.  The handle_<event> handlers can the overridden to override the
behaviour of the Client class, though this is not recommended.

The subclassing method allows separation of the instance of the client
and the code that handles it.  (i.e. you don't need the instance of the
client object to define event handlers for it).  Though, the old method
of using the event decorator from the instance will still be supported.

discord/client.py

@@ -216,6 +216,24 @@ class Client(object):
         else:
             return []
 
+    def on_error(self, event_method, *args, **kwargs):
+        msg = 'Caught exception in {} with args (*{}, **{})'
+        log.exception(msg.format(event_method, args, kwargs))
+
+    def dispatch(self, event, *args, **kwargs):
+        log.debug("Dispatching event {}".format(event))
+        handle_method = '_'.join(('handle', event))
+        event_method = '_'.join(('on', event))
+        getattr(self, handle_method, _null_event)(*args, **kwargs)
+        try:
+            getattr(self, event_method, _null_event)(*args, **kwargs)
+        except Exception as e:
+            getattr(self, 'on_error')(event_method, *args, **kwargs)
+
+        # Compatibility shim to old event system.
+        if event_method in self.events:
+            self._invoke_event(event_method, *args, **kwargs)
+
     def _invoke_event(self, event_name, *args, **kwargs):
         try:
             log.info('attempting to invoke event {}'.format(event_name))
@@ -230,7 +248,7 @@ class Client(object):
         if response.get('op') != 0:
             return
 
-        self._invoke_event('on_response', response)
+        self.dispatch('response', response)
         event = response.get('t')
         data = response.get('d')
 
@@ -250,18 +268,18 @@ class Client(object):
             self.keep_alive.start()
 
             # we're all ready
-            self._invoke_event('on_ready')
+            self.dispatch('ready')
         elif event == 'MESSAGE_CREATE':
             channel = self.get_channel(data.get('channel_id'))
             message = Message(channel=channel, **data)
-            self._invoke_event('on_message', message)
+            self.dispatch('message', message)
             self.messages.append(message)
         elif event == 'MESSAGE_DELETE':
             channel = self.get_channel(data.get('channel_id'))
             message_id = data.get('id')
             found = self._get_message(message_id)
             if found is not None:
-                self._invoke_event('on_message_delete', found)
+                self.dispatch('message_delete', found)
                 self.messages.remove(found)
         elif event == 'MESSAGE_UPDATE':
             older_message = self._get_message(data.get('id'))
@@ -277,7 +295,7 @@ class Client(object):
                         setattr(message, attr, utils.parse_time(value))
                     else:
                         setattr(message, attr, value)
-                self._invoke_event('on_message_edit', older_message, message)
+                self.dispatch('message_edit', older_message, message)
                 # update the older message
                 older_message = message
 
@@ -295,8 +313,8 @@ class Client(object):
                     member.avatar = user.get('avatar', member.avatar)
 
                     # call the event now
-                    self._invoke_event('on_status', member)
-                    self._invoke_event('on_member_update', member)
+                    self.dispatch('status', member)
+                    self.dispatch('member_update', member)
         elif event == 'USER_UPDATE':
             self.user = User(**data)
         elif event == 'CHANNEL_DELETE':
@@ -305,14 +323,14 @@ class Client(object):
                 channel_id = data.get('id')
                 channel = utils.find(lambda c: c.id == channel_id, server.channels)
                 server.channels.remove(channel)
-                self._invoke_event('on_channel_delete', channel)
+                self.dispatch('channel_delete', channel)
         elif event == 'CHANNEL_UPDATE':
             server = self._get_server(data.get('guild_id'))
             if server is not None:
                 channel_id = data.get('id')
                 channel = utils.find(lambda c: c.id == channel_id, server.channels)
                 channel.update(server=server, **data)
-                self._invoke_event('on_channel_update', channel)
+                self.dispatch('channel_update', channel)
         elif event == 'CHANNEL_CREATE':
             is_private = data.get('is_private', False)
             channel = None
@@ -327,18 +345,18 @@ class Client(object):
                     channel = Channel(server=server, **data)
                     server.channels.append(channel)
 
-            self._invoke_event('on_channel_create', channel)
+            self.dispatch('channel_create', channel)
         elif event == 'GUILD_MEMBER_ADD':
             server = self._get_server(data.get('guild_id'))
             member = Member(server=server, deaf=False, mute=False, **data)
             server.members.append(member)
-            self._invoke_event('on_member_join', member)
+            self.dispatch('member_join', member)
         elif event == 'GUILD_MEMBER_REMOVE':
             server = self._get_server(data.get('guild_id'))
             user_id = data['user']['id']
             member = utils.find(lambda m: m.id == user_id, server.members)
             server.members.remove(member)
-            self._invoke_event('on_member_remove', member)
+            self.dispatch('member_remove', member)
         elif event == 'GUILD_MEMBER_UPDATE':
             server = self._get_server(data.get('guild_id'))
             user_id = data['user']['id']
@@ -354,21 +372,21 @@ class Client(object):
                     if role.id in data['roles']:
                         member.roles.append(role)
 
-                self._invoke_event('on_member_update', member)
+                self.dispatch('member_update', member)
         elif event == 'GUILD_CREATE':
             self._add_server(data)
-            self._invoke_event('on_server_create', self.servers[-1])
+            self.dispatch('server_create', self.servers[-1])
         elif event == 'GUILD_DELETE':
             server = self._get_server(data.get('id'))
             self.servers.remove(server)
-            self._invoke_event('on_server_delete', server)
+            self.dispatch('server_delete', server)
 
     def _opened(self):
         log.info('Opened at {}'.format(int(time.time())))
 
     def _closed(self, code, reason=None):
         log.info('Closed with {} ("{}") at {}'.format(code, reason, int(time.time())))
-        self._invoke_event('on_disconnect')
+        self.dispatch('disconnect')
 
     def run(self):
         """Runs the client and allows it to receive messages and events."""