simple subreddit converter example in discord.py

converters.py

class Subreddit(commands.Converter):
	async def convert(self, arg):
		if arg.startswith("r/"):
			arg = arg[2:]
		return arg

@client.command()
async def convert(ctx, subreddit: Subreddit): # use a typehint to specify converter
	await ctx.send(subreddit)

# if we invoke the convert command with "r/testsubreddit"
# it will send back "testsubreddit" and if we invoke it with
# "testsubreddit" the output will stay the same as the input.