[Sync Iteration] python/isogram/3

Author: exercism-solutions-syncer[bot]

solutions/python/isogram/3/isogram.py

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+"""
+Isogram.
+
+Determine if a word or phrase is an isogram.
+
+An isogram (also known as a "non-pattern word") is a word or phrase
+without a repeating letter, however spaces and hyphens are allowed
+to appear multiple times.
+
+Examples of isograms:
+
+lumberjacks
+background
+downstream
+six-year-old
+
+The word isograms, however, is not an isogram, because the s repeats.
+"""
+
+
+def is_isogram(string: str) -> bool:
+    """
+    Determine if a word or phrase is an isogram.
+
+    An isogram is a word or phrase without repeating letters. Spaces and hyphens
+    are allowed to appear multiple times, but alphabetic characters must be unique
+    (case-insensitive).
+
+    :param string: The word or phrase to check
+    :type string: str
+    :returns: True if the string is an isogram, False otherwise
+    :rtype: bool
+    """
+    # empty string
+    if not string:
+        return True
+
+    letters: list[str] = [char for char in string.lower() if char.isalpha()]
+    return len(letters) == len(set(letters))