Types of Handlers

A Handler is an instance derived from the base class telegram.ext.Handler which is responsible for the routing of different kinds of updates (text, audio, inlinequery, button presses, ...) to their corresponding callback function in your code.

For example, if you want your bot to respond to the command /start, you can use a telegram.ext.CommandHandler that maps this user input to a callback named start_callback:

async def start_callback(update, context):
    await update.message.reply_text("Welcome to my awesome bot!")

...

application.add_handler(CommandHandler("start", start_callback))

Different types of Updates

For different kinds of user input, the received telegram.Update will have different attributes set. For example an incoming message will result in update.message containing the sent message. The pressing an inline button will result in update.callback_query being set. To differentiate between all those updates, telegram.ext provides

1. telegram.ext.MessageHandler for all message updates
2. telegram.ext.CommandHandler for messages with bot commands
3. multiple handlers for all the other different types of updates, e.g. telegram.ext.CallbackQueryhandler for update.callback_query and telegram.ext.InlineQueryHandler for update.inline_query
4. A few more handlers for more advanced use cases

The special thing about MessageHandler is that there is such a vast variety of message types (text, gif, image, document, sticker, …) that it's infeasible to provide a different Handler for each type. Instead MessageHandler is coupled with so called filters that allow to make fine-grained distinctions: MessageHandler(filters.ALL, callback) will handle all updates that contain

• update.message
• update.edited_message
• update.channel_post
• update.edited_channel_post

You can use the different filters to narrow down which updates your MessageHandler will handle. See also this article for advanced usage of filters.

Because bot commands are another special part of the user interface of bots, there is the dedicated CommandHandler, which allows you to easily handle messages like /start or /help. Of course those messages can also be handled with MessageHandler, if needed.

CommandHandlers with arguments

It is also possible to work with parameters for commands offered by your bot. Let's extend the start_callback with some arguments so that the user can provide additional information in the same step:

async def start_callback(update, context):
    user_says = " ".join(context.args)
    await update.message.reply_text("You said: " + user_says)

...

application.add_handler(CommandHandler("start", start_callback))

Sending /start Hello World! to your bot will now split everything after /start separated by the space character into a list of words and pass it on to the args attribute of context: ["Hello", "World!"]. We join these chunks together by calling " ".join(context.args) and echo the resulting string back to the user.

Deep-Linking start parameters

The argument passing described above works exactly the same when the user clicks on a deeply linked start URL, like this one:

https://t.me/roolsbot?start=Hello_World!

Clicking this link will open your Telegram Client and show a big START button. When it is pressed, the URL parameters "Hello_World!" will be passed on to the args of your context object.

Note that since telegram doesn't support spaces in deep linking parameters, you will have to manually split the single Hello_World argument, into ["Hello", "World!"] (using context.args[0].split('_') for example)

You also have to pay attention to the maximum length accepted by Telegram itself. As stated in the documentation the maximum length for the start parameter is 64.

Also, since this is an URL parameter, you have to pay attention on how to correctly pass the values in order to avoid passing URL reserved characters. Consider the usage of base64.urlsafe_b64encode.

Pattern matching: filters.Regex

For more complex inputs you can employ the telegram.ext.MessageHandler with telegram.ext.filters.Regex, which internally uses the re-module to match textual user input with a supplied pattern.

Keep in mind that for extracting URLs, #Hashtags, @Mentions, and other Telegram entities, there's no need to parse them with a regex filter because the Bot API already sends them to us with every update. Refer to this snippet to learn how to work with entities instead.

This tutorial only covers some of the available handlers (for now). Refer to the documentation for all other types: https://python-telegram-bot.readthedocs.io/en/latest/telegram.ext.html#handlers

Custom updates

In some cases, it's useful to handle updates that are not from Telegram. E.g. you might want to handle notifications from a 3rd party service and forward them to your users. For such use cases, PTB provides

• TypeHandler
• StringCommandHandler
• StringRegexHandler

See also this FAQ entry