1. Calculate the normalized letter frequencies. In order to calculate letter frequencies, you need a list of letters and the string in all upper-case letters. To avoid confusion, we will rename this built-in string ascii_uppercase as alphabet when we import it. : #grade from string import ascii_uppercase as alphabet # use \alphabet' as ascii_uppercase from now on print(alphabet) : #grade # Our example text. text = 'Jackdaws love my big Sphinx of Quartz.' text = text.upper() print(text) Next we create an empty frequency dictionary letter_freq. Loop over each letter of the alphabet and count the number of times each letter occurs in text. Add this count to letter_freq #grade letter_freq {} # a blank dictionary # Loop over the alphabet. for letter in alphabet: # For each letter, get the number of times it occurs in the string 'text. letter_count = text.count(letter) letter_freq[letter] = letter_count letter_freq The final step is to normalize the values. To do this, we need to calculate the total number of letters in text (letters, NOT whitespace or punctuation). Since this is a bit involved, the following lines of code will give us a copy of text without whitespace or punctuation: #grade # These are built-in collections of characters, useful for just this sort of filtering from string import whitespace, punctuation, digits print(whitespace, punctuation, digits) for character in whitespace+punctuation+digits: text = text.replace(character, '') Now set each frequency value in the dictionary to its normalized value. #grade for key in letter_freq.keys(): letter_freq[key] = letter_freq[key] / len(text) letter_freq Now we will turn the above process into a general function to process a string into its letter frequency