code: def _starting_consonants_only(self, letters: list) -> list:
          
          for idx, letter in enumerate(letters):
              if not self._contains_vowels(letter) and self._contains_consonants(letter):
                  return [idx]
              if self._contains_vowels(letter):
                  return []
              if self._contains_vowels(letter) and self._contains_consonants(letter):
                  return []
          return []
docs: Return a list of starting consonant positions.