def _long_by_nature(self, syllable):
        """Check if syllable is long by nature. Long by nature includes:
        1) Syllable contains a diphthong
        2) Syllable contains a long vowel
        :param syllable: current syllable
        :return: True if long by nature
        :rtype : bool
        """

        # Find diphthongs
        vowel_group = ''
        for char in syllable:
            if char in self.long_vowels:
                return True
            elif char not in self.sing_cons:
                vowel_group += char

        if vowel_group in self.diphthongs:
            return True
Check if syllable is long by nature. Long by nature includes:
        1) Syllable contains a diphthong
        2) Syllable contains a long vowel
        :param syllable: current syllable
        :return: True if long by nature
        :rtype : bool