Migrating from python-telegram-bot

Let’s take their echobot.py example and shorten it a bit:

from telegram.ext import Updater, CommandHandler, MessageHandler, Filters

def start(update, context):
    """Send a message when the command /start is issued."""
    update.message.reply_text('Hi!')

def echo(update, context):
    """Echo the user message."""
    update.message.reply_text(update.message.text)

def main():
    """Start the bot."""
    updater = Updater("TOKEN")
    dp = updater.dispatcher
    dp.add_handler(CommandHandler("start", start))
    dp.add_handler(MessageHandler(Filters.text & ~Filters.command, echo))

    updater.start_polling()

    updater.idle()

if __name__ == '__main__':
    main()

After using Telethon:

from telethon import TelegramClient, events

bot = TelegramClient('bot', 11111, 'a1b2c3d4').start(bot_token='TOKEN')

@bot.on(events.NewMessage(pattern='/start'))
async def start(event):
    """Send a message when the command /start is issued."""
    await event.respond('Hi!')
    raise events.StopPropagation

@bot.on(events.NewMessage)
async def echo(event):
    """Echo the user message."""
    await event.respond(event.text)

def main():
    """Start the bot."""
    bot.run_until_disconnected()

if __name__ == '__main__':
    main()

Key differences:

• The recommended way to do it imports less things.
• All handlers trigger by default, so we need events.StopPropagation.
• Adding handlers, responding and running is a lot less verbose.
• Telethon needs async def and await.
• The bot isn’t hidden away by Updater or Dispatcher.