Two Telegram clients and one tiny forwarding bot

Sometimes the best automation is a small one. This job started with a single sentence from a client, and it turned into a neat little Telegram project.

The goal

The client wanted any message sent by a particular bot on Telegram to be forwarded to them by another bot, so they could run analysis on it. They also wanted it written in Python 3.

The solution

Telethon is an asynchronous Python library that can do just about everything we need:

• Log in as a user
• Log in as a bot
• Listen for events, and filter them
• Send messages

That matters because this job needs two clients. A user client acts as the ears, noticing when a message arrives. A bot client acts as the mouth, sending it onward.

With both connected, the events.NewMessage handler does the rest. We filter by channel and sender, and when a message matches our edge case, we can do whatever we like with it.

Here, we take the raw_text from the event and have the bot client send it on.

The nice part is the room to grow. Once you have the message in hand, forwarding is just the first thing you could do with it.

The proof of concept

This is what the event handling looks like:

@user_client.on(
    events.NewMessage(
        incoming=True,
        from_users=Config.USER_TO_LISTEN_TO,
    )
)
async def handler(event: events.NewMessage.Event):
    logger.info(f"Received message: {event.raw_text}")
    await bot_client.send_message(Config.USER_TO_FORWARD_TO, event.raw_text)

    logger.info(f"Forwarded message: {event.raw_text}")

A decorator, a filter and one send_message call. That's the whole trick.

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See the code

The repo has two branches:

• main is the simple version.
• verbose adds thorough error handling and a properly managed asynchronous event loop.