title: Python create all pairs of letters from abcdefghijkl... letter string
body: <pre><code>import string
  letters=string.ascii_lowercase
  letters
  
  'abcdefghijklmnopqrstuvwxyz'
  </code></pre>
  <p>we are looking to convert <code>letters</code> into a list of length 26^2, featuring all unordered pairings of letters <code>['aa', 'ab', 'ac', ..., 'az', 'ba', 'bb', 'bc', ..., 'zz']</code>. I am looking to avoid code that looks like this:</p>
  <pre><code>letter_list = []
  for letter1 in letters:
      for letter2 in letters:
          letter_list.append(f'{letter1}{letter2}')
  </code></pre>
  <p>Is there a 1 liner with nested list comprehension?</p>