

7. Reacting to Commands

The next thing we are going to do is to make our bot respond to commands. To start off, we need to initialise the updater.

from telegram.ext import Updater
updater = Updater(token='YOUR TOKEN HERE')
dispatcher = updater.dispatcher

The crucial part is defining the functions that allows us to specify what the bot does upon receiving a command. The function should contain the parameters bot and update so that you can reference the bot and the update within the function definition.

def start(bot, update):
    message = "Hello, " + update.message.from_user.first_name
    bot.send_message(chat_id=update.message.chat_id, text=message)

Next, we have to create a CommandHandler and then add it to the dispatcher.

from telegram.ext import CommandHandler

start_handler = CommandHandler("start", start)
# create a CommandHandler that responds to the command "/start" and runs the function start
dispatcher.add_handler(start_handler)
# add this handler to the dispatcher

Finally, to get our bot to start running, we write the following lines:

updater.start_polling()
updater.stop()

Now, let's try to write a CommandHandler that can take in some user input. To do this, when creating our CommandHandler, we must set pass_args to True (this is an optional parameter). The function will then receive the user input as a list of values seperated by spaces. For example, if we type "/add 2 2" to our bot, it will take in args as a list [2, 2].

def add(bot, update, args):
    # args is a list [1st no, 2nd no]
    first_no = int(args[0])
    second_no = int(args[1])
    number = first_no + second_no
    result = number * number
    bot.send_message(chat_id=update.message.chat_id, text=str(result))

sum_handler = CommandHandler("add", add, pass_args=True)
dispatcher.add_handler(sum_handler)

Now, try writing a handler that will raise the first number to the power of the second, using a while loop (do not use **). For example, if I type /power 2 4, the bot should say 16.