title: How do you require an input to validate as an integer with 10 digits?
body: <p>I am making an ISBN check digit program. However, although I have made my program so that it will only accept a value of length 10, if I input 10 letters it will crash. </p>
  
  <p>Does anyone know how to fix this?</p>
  
  <p>My Code:</p>
  
  <pre><code>isbnnumber = input('Please input your 10 digit book no. : ')
  while len(isbnnumber) != 10:
      print('You have not entered a 10 digit value! Please try again.')
      isbnnumber = input('Please input your 10 digit book no. : ')
  else:
      no1 = int(isbnnumber[0])*11
      no2 = int(isbnnumber[1])*10... etc...
  </code></pre>
  
  <p>Help would be very much appreciated, thanks.</p>