docs: def _candidate_filenames():
      """Generates filenames of the form 'specktre_123AB.png'.
  
      The random noise is five characters long, which allows for
      62^5 = 916 million possible filenames.
  
      """
      while True:
          random_stub = ''.join([
              random.choice(string.ascii_letters + string.digits)
              for _ in range(5)
          ])
          yield 'specktre_%s.png' % random_stub