bot: add error handler

bot.py

@@ -1,9 +1,15 @@
 #!/usr/bin/env python3
 # encoding: utf-8
 
+import logging
+
 import discord
 from discord.ext import commands
 
+logging.basicConfig(level=logging.WARNING)
+logger = logging.getLogger(__name__)
+logger.setLevel(logging.INFO)
+
 class Bot(commands.AutoShardedBot):
 	def __init__(self, **kwargs):
 		super().__init__(command_prefix=commands.when_mentioned, **kwargs)
@@ -18,8 +24,29 @@ class Bot(commands.AutoShardedBot):
 		super().run(self.config['tokens'].pop('discord'))
 
 	async def on_ready(self):
-		print('Logged on as {0} (ID: {0.id})'.format(self.user))
+		logger.info('Logged on as {0} (ID: {0.id})'.format(self.user))
 
+	# https://github.com/Rapptz/RoboDanny/blob/ca75fae7de132e55270e53d89bc19dd2958c2ae0/bot.py#L77-L85
+	async def on_command_error(self, context, error):
+		if isinstance(error, commands.NoPrivateMessage):
+			await context.author.send('This command cannot be used in private messages.')
+		elif isinstance(error, commands.DisabledCommand):
+			message = 'Sorry. This command is disabled and cannot be used.'
+			try:
+				await context.author.send(message)
+			except discord.Forbidden:
+				await context.send(message)
+		elif isinstance(error, commands.UserInputError):
+			await context.send(error)
+		elif isinstance(error, commands.NotOwner):
+			logger.error('%s tried to run %s but is not the owner', context.author, context.command.name)
+		elif isinstance(error, commands.CommandInvokeError):
+			await context.send('An internal error occured while trying to run that command.')
+
+			logger.error('In %s:', context.command.qualified_name)
+			logger.error(''.join(traceback.format_tb(error.original.__traceback__)))
+			# pylint: disable=logging-format-interpolation
+			logger.error('{0.__class__.__name__}: {0}'.format(error.original))
 
 bot = Bot()