"""
An isogram is a word that has no repeating letters, consecutive or non-consecutive. Implement a function that determines whether a string that contains only letters is an isogram. Assume the empty string is an isogram. Ignore letter case.

Example: (Input --> Output)

"Dermatoglyphics" --> true
"aba" --> false
"moOse" --> false (ignore letter case)
"""

def is_isogram(string):
    string = string.lower()
    for letter in string:
        if string.count(letter) > 1:
            return False
    return True

# Solution la plus opti

def is_isogram(string):
    return len(string) == len(set(string.lower()))