Given the phones in a syllable, retrieves the vowel index

def _getSyllableNucleus(phoneList):
    '''
    Given the phones in a syllable, retrieves the vowel index
    '''
    cvList = ['V' if isletool.isVowel(phone) else 'C' for phone in phoneList]
    
    vowelCount = cvList.count('V')
    if vowelCount > 1:
        raise TooManyVowelsInSyllable(phoneList, cvList)
    
    if vowelCount == 1:
        stressI = cvList.index('V')
    else:
        stressI = None
        
    return stressI