title: How can I create words with a certain length consisting of a and b?
body: <p>I want to create a list of all words with a certain length (for example 1 to 3) that consist of two letters. So my output would be: 
  a, b, aa, ab, ba, bb,.... 
  but I am struggling to implement it recursively in python. What’s the right way to do this? </p>