import string
+import collections
def caesar_cipher_letter(letter, shift):
def caesar_decipher_message(message, shift):
return caesar_cipher_message(message, -shift)
+
+def letter_frequencies(message):
+ frequencies = collections.defaultdict(int)
+ for letter in message:
+ if letter in string.ascii_letters:
+ frequencies[letter.lower()]+=1
+ return frequencies
+