print count_words("betty bought a bit of butter but the butter was bitter",3)

[('butter', 2), ('a', 1), ('betty', 1)]

"""Count words."""

def count_words(s, n):
  """Return the n most frequently occuring words in s."""
  w = {}
  sp = s.split()
  # TODO: Count the number of occurences of each word in s
  for i in sp:
    if i not in w:
      w[i] = 1
    else:
      w[i] += 1

  # TODO: Sort the occurences in descending order (alphabetically in case of ties)
  top = sorted(w.items(), key=lambda item:(-item[1], item[0]))
  top_n = top[:n]
  # TODO: Return the top n most frequent words.
  return top_n


def test_run():
  """Test count_words() with some inputs."""
  print count_words("cat bat mat cat bat cat", 3)
  print count_words("betty bought a bit of butter but the butter was bitter", 3)


if __name__ == '__main__':
  test_run()