title: Find chat_id in python-telegram-bot
body: <p>I tried to create a bot in telegram with python, bot I can't find <code>chat_id</code>.
  What should I do?</p>
  <p>My code:</p>
  <pre><code>from telegram.ext import Updater, CommandHandler
  from telegram import ReplyKeyboardMarkup
  
  updater = Updater(Token)
  def start(update, _) :
      update.message.reply_text('Hello {}'.format(update.message.chat.first_name))
  
  def service_keyboards(bot,update) :
      chat_id = update.message.chat_id
      keyboard = [['Send Video'], ['Send Music']]
      bot.sendMessage(chat_id, 'Plese choose an item.', reply_markup = ReplyKeyboardMarkup(keyboard))
  
  start_command = CommandHandler('start' , start)
  service_command = CommandHandler('service' , service_keyboards)
  updater.dispatcher.add_handler(start_command)
  updater.dispatcher.add_handler(service_command)
  updater.start_polling()
  updater.idle()
  </code></pre>
  <p>Eror:</p>
  <blockquote>
  <p>No error handlers are registered, logging exception. Traceback (most
  recent call last):   File
  &quot;c:\users\Ghazal\appdata\local\programs\python\python38\lib\site-packages\telegram\ext\dispatcher.py&quot;,
  line 442, in process_update
  handler.handle_update(update, self, check, context)   File &quot;c:\users\Ghazal\appdata\local\programs\python\python38\lib\site-packages\telegram\ext\handler.py&quot;,
  line 160, in handle_update
  return self.callback(update, context)   File &quot;&quot;, line 9, in start
  chat_id = update.message.chat_id AttributeError: 'CallbackContext' object has no attribute 'message'</p>
  </blockquote>