Python/strings/is_isogram.py

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"""
wiki: https://en.wikipedia.org/wiki/Heterogram_(literature)#Isograms
"""
def is_isogram(string: str) -> bool:
"""
An isogram is a word in which no letter is repeated.
Examples of isograms are uncopyrightable and ambidextrously.
>>> is_isogram('Uncopyrightable')
True
>>> is_isogram('allowance')
False
>>> is_isogram('copy1')
Traceback (most recent call last):
...
ValueError: String must only contain alphabetic characters.
"""
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.")