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 CommandHandler that maps this user input to a callback named start_callback:

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

...

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

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:

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

...

dispatcher.add_handler(CommandHandler("start", start_callback, pass_args=True))```

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` parameter of `start_callback`: `["Hello", "World!"]`. We join these chunks together by calling `" ".join(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%20World!

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 /start callback.


## Pattern matching: The RegexHandler

For more complex inputs you can employ the [telegram.ext.RegexHandler](https://python-telegram-bot.readthedocs.io/en/latest/telegram.ext.regexhandler.html), which internally uses the `re`-module to match textual user input with a supplied pattern.

A quick example:

Keep in mind that for extracting URLs, #Hashtags, @Mentions, and other Telegram entities, there's no need to parse them with a `RegexHandler` because the Bot API already sends them to us with every update. Refer to [this snippet](https://github.com/python-telegram-bot/python-telegram-bot/wiki/Code-snippets#message-entities) to learn how to work with entities instead.


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