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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _ending_consonants_only(self, letters: List[str]) -> List[int]: """Return a list of positions for ending consonants."""

        reversed_letters = list(reversed(letters))
        length = len(letters)
        for idx, letter in enumerate(reversed_letters):
            if not self._contains_vowels(letter) and self._contains_consonants(letter):
                return [(length - idx) - 1]
            if self._contains_vowels(letter):
                return []
            if self._contains_vowels(letter) and self._contains_consonants(letter):
                return []
        return []