title: Defining Function Python
body: <p>I'm trying to write a function that has one parameter that returns True if all the characters in the string are upper case or lower case ASCII letters, and the string is not empty. I want it to return False otherwise. I can tell I'm doing this all wrong. </p>
  
  <pre><code>ASCII_LOWERCASE = "abcdefghijklmnopqrstuvwxyz"
  ASCII_UPPERCASE = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  DECIMAL_DIGITS = "0123456789"
  
  
  def is_alpha(a_string):   
      if a_string in ASCII_LOWERCASE or ASCII_UPPERCASE:
              for i in ASCII_LOWERCASE or ASCII_UPPERCASE:
              return "True"
  </code></pre>