wiki https en wikipedia orgwikiheterogramliteratureisograms an isogram is a word in which no letter is repeated examples of isograms are unable and ambidextrously isisogram unable true isisogram allowance false isisogram copy1 traceback most recent call last valueerror string must only contain alphabetic characters an isogram is a word in which no letter is repeated examples of isograms are unable and ambidextrously is_isogram unable true is_isogram allowance false is_isogram copy1 traceback most recent call last valueerror string must only contain alphabetic characters
def is_isogram(string: str) -> bool:
    
    if not all(x.isalpha() for x in string):
        raise ValueError("String must only contain alphabetic characters.")

    letters = sorted(string.lower())
    return len(letters) == len(set(letters))


if __name__ == "__main__":
    input_str = input("Enter a string ").strip()

    isogram = is_isogram(input_str)
    print(f"{input_str} is {'an' if isogram else 'not an'} isogram.")