title: Python - Validation to ensure input only contains characters A-Z
body: <p>I'm creating a program in Python 3.x where it asks the user for their first name and then last name and stores these in variables which are then concatenated into one variable:</p>
  
  <pre><code>firstName = input("What's your first name? ")
  lastName = input("What's your first name? ")
  name = firstName + " " + lastName
  </code></pre>
  
  <p>I tried:</p>
  
  <pre><code>while True:
      try:
          firstName = input("What's your first name? ")
          lastName = input("What's your first name? ")
          name = firstName + " " + lastName
          break
      except ValueError:
          print("That's invalid, please try again.")
  </code></pre>
  
  <p>which ensures that a string is inputted, but inputting 'bob38', '74' or '][;p/' all count as string values, so these would be accepted, which is not what I want to happen.</p>
  
  <p>I want valid input to only contain the letters A-Z/a-z (both uppercase and lowercase), and if the input contains anything else, an error message is outputted (e.g. 'That's invalid, try again.') and the user is asked the question again. How would I do this?</p>