title: How to check for a necessary input of raw_input?
body: <p>I've started to learn python only a day ago, seems to be easy, but still have some questions :)</p>
  
  <p>how to write a script which have to check necessary input of raw_input?</p>
  
  <p>I mean, the script must stop if a user have not entered any case and just hit enter on raw_input...</p>