title: How to obtain username from UserID in Telegram?
body: <p>I am using <a href="https://github.com/python-telegram-bot/python-telegram-bot" rel="nofollow noreferrer">Python-Telegram-Bot</a> API to create a bot. I get people's userID and username when they start the bot.<br>
  The userID doesn't change ever but the username can be changed by the user any time.<br>
  So I have usernames and UserIDs, and I receive another username - I wish to figure out whether that username is of someone already in the existing list or not.<br>
  Basically need to find out username from userID or if there's any other way I'm open to it.</p>