Exercise from CodeWars

Duplicate Count

from collections import Counter


def duplicate_count(text):
    """Write a function that will return the count of distinct case-insensitive alphabetic characters and numeric
    digits that occur more than once in the input string. The input string can be assumed to contain only alphabets (
    both uppercase and lowercase) and numeric digits. """
    return sum([1 for a in Counter(text.lower()).values() if a > 1])


duplicate_count("abcde"), 0
duplicate_count("abcdea"), 1
duplicate_count("Indivisibilities"), 1
duplicate_count("abcdefghijklmnopqrstuvwxyz"), 2