title: infinite while loop issue on dice roll program
body: <p>I have made this code for a project and i have run into a problem with the while loop becasue it just repeat the first input function, here is the code, i would aprriecate it if someone could  point out my problem and help me fix my code, thnx </p>
  
  <pre><code>import random
  roll_agn='yes'
  while roll_agn=='yes':
      dice=input ('Please choose a 4, 6 or 12 sided dice: ')
      if dice ==4:
          print(random.randint(1,4))
      elif dice ==6:
          print(random.randint(1,6))
      elif dice ==12:
          print(random.randint(1,12))
      else:
          roll_agn=input('that is not 4, 6 or 12, would you like to choose again, please answer yes or no') 
      if roll_agn !='yes':
          print ('ok thanks for playing')
  </code></pre>