Telebot Basics

Commands

Commands in Telegram are messages that start with a slash "/" followed by the command name

e.g. /start or /help

We define a few commands.

• These usually take in two arguments "update" and "context"

/start Command

Sends a message when the command /start is issued

async def start(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
    user = update.effective_user
    await update.message.reply_text(text=f'Hello {user.mention_markdown_v2()}\!'
                                         f'\nEnter /help to see the list of '
                                         f'commands for this bot\.',
                                    parse_mode=ParseMode.MARKDOWN_V2)

Your Output will look something like this:

Hello 'Username'! #replaced by your username Enter /help to see the list of commands for this bot.

Code Explanation

• user = update.effective_user extracts information about the user

• parse_mode=ParseMode.MARKDOWN_V2 means your telebot will use Telegram's MarkdownV2 formatting for the message

• user.mention_markdown_v2() is a function that ensures the user is mentioned and displayed correctly

/error Command

The error function is an error handler for your Telegram Bot. It is designed to log and print information about errors during the bot's operation.

async def error(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
    print(f'Update {update} caused error {context.error}')

• Update {update} : Includes information about the update (user input) that was processed when the error occurred

• caused error {context.error} : Information about the error that was raised

Now, let us move on to something more "custom" for our telebot. Like a quadratic formula!

Custom Commands

Creating a quadratic formula command

The Formula:

import math

async def quadratic(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
    
    # extract the message from the user input
    # e.g. /quadratic 1 2 3
    message = update.message.text
    
    # assign each number input to a string
    # e.g. a_string = 1, b_string = 2, c_string = 3
    _, a_string, b_string, c_string = message.split()
    
    # convert from a string to a float
    a = float(a_string)
    b = float(b_string)
    c = float(c_string)
    
    # Calculate the discriminant
    disc = b**2 - 4*a*c

    # Assume 2 real solutions and calculate the roots 
    # Can add conditional statements for imaginary solution etc.
    root1 = (-b + math.sqrt(disc)) / 2*a
    root2 = (-b - math.sqrt(disc)) / 2*a

    # Create the reply text
    reply = f"Your roots are {root1} and {root2}"
    
    update.message.reply_text(reply)
    

Initialising and Command Handling

1. First, Initialise the Bot with your Token

• We do this using the 'Application' class from the 'python-telegram-bot' library

• The TOKEN is your unique bot token obtained from BotFather

if __name__ == '__main__':
    app = Application.builder().token(TOKEN).build()

2. Register Command Handlers

• When a user sends /start the 'start' function will be executed

• When a user sends /help the 'help' function will be executed

• When a user sends /quadratic the 'quadratic' function will be executed

    app.add_handler(CommandHandler('start', start))
    app.add_handler(CommandHandler('help', help))
    app.add_handler(CommandHandler('quadratic', quadratic))

3. Register Message Handler

• Processes all text messages

• When a user sends a text message, the 'handle_message' function will be executed

    app.add_handler(MessageHandler(filters.TEXT, handle_message))

4. Register Error Handler

• Handle error's during a telebot's opertation. If an error occurs, the 'error' function will be executed

    app.add_error_handler(error)

5. Now, Start Polling

• Prints 'Polling...' to the console to indicate that the bot is starting

• Polling is a method for the bot to continuously check for new updates from Telegram

    print('Polling...')
    asyncio.run(app.run_polling())

6. Putting it all together

Your code should look something like this:

if __name__ == '__main__':
    app = Application.builder().token(TOKEN).build()

    app.add_handler(CommandHandler('start', start))
    app.add_handler(CommandHandler('help', help))
    app.add_handler(CommandHandler('quadratic', quadratic))

    app.add_handler(MessageHandler(filters.TEXT, handle_message))

    app.add_error_handler(error)

    print('Polling...')
    asyncio.run(app.run_polling())