from collections import Counter


def count_letters(filename):
    letter_counter = Counter()
    with open(filename) as file:
        for line in file:
            line_letters = [char for char in line.lower() if char.isalpha()]

            letter_counter.update(Counter(line_letters))
    return letter_counter


letter_counter = count_letters("wc.py")
for letter, count in letter_counter.items():
    print(letter, "->", count)

print("most_common(5)")
for letter, count in letter_counter.most_common(5):
    print(letter, "->", count)