We can also use format() to treat vowel harmony. Choose a simplevowel harmony system and show how this might work.

Vowel harmony is a phonological process where the vowels of a word must share certain characteristics. A simple example of a vowel harmony system is found in Finnish language. In Finnish, vowels are divided into two groups: front vowels (ä, ö, y) and back vowels (a, o, u). A word cannot contain both front and back vowels.

Here's how you might use the format() function in Python to enforce this rule:

def vowel_harmony(word):
    front_vowels = "äöy"
    back_vowels = "aou"
    for char in word:
        if char in front_vowels and any((vowel in word) for vowel in back_vowels):
            return "Word does not follow vowel harmony"
        if char in back_vowels and any((vowel in word) for vowel in front_vowels):
            return "Word does not follow vowel harmony"
    return "Word follows vowel harmony"

print(vowel_harmony("sauna"))  # Word follows vowel harmony
print(vowel_harmony("säuna"))  # Word does not follow vowel harmony

In this code, we define a function vowel_harmony() that checks if a word follows the vowel harmony rule. It iterates over each character in the word. If it finds a front vowel, it checks if there are any back vowels in the word, and vice versa. If it finds a violation of the rule, it returns a message saying that the word does not follow vowel harmony. If it doesn't find any violations, it returns a message saying that the word follows vowel harmony.