title: How to convert a string into ASCII?
body: <p>How can I convert a string, say <code>"HELLO"</code>, into something like this?</p>
  
  <p>As ASCII string: <code>"72_69_76_76_79"</code>. </p>
  
  <p>I tried <code>[ord(c) for c in string]</code>, but it returns a list. </p>
  
  <p>I want the result in the form of string </p>