A script to auto reply private messages on telegram with a fixed message. It's simple to modify and make it respond to group/channel messages as well. Check the Telethon documentation.
You only need to get the api_id and the api_hash from the Telegram Core. After you create your new app, you'll have access to these items.
You just need to replace these items in the right places, put your username (your nickname without @) in the 'Username' location, choose the automatic message to show when someone sends you a message and run the program. It will be waiting for a private message to reply it.
api_id = 'put your api_id here'
api_hash = 'put yout api_hash here'
client = TelegramClient('Username', api_id, api_hash)
message = 'Hey, I'll be at a retreat until Saturday. I promise to get in touch as soon as I can. See you.'