from string import ascii_lowercase


LOWERCASE = set(ascii_lowercase)


def is_isogram(s):
    chars = [c for c in s.lower() if c in LOWERCASE]
    return len(chars) == len(set(chars))

@@ -178,8 +178,159 @@
 chars))%0A
+%0A%0A# You could also achieve this using %22c.isalpha()%22 instead of LOWERCASE%0A# You would then not need to import from %60string%60, but it's marginally slower%0A

Add note about str.isalpha() method as an alternative