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diff --git a/‎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.")