count unique letters in a word

[kotter]

Maybe you understand this code better:

# write function that counts number of unique english letters
def unique_english_letters(word):
    var1 = [y for y in word if y.isalpha()] #list containing only letters of given string
    var2 = list(set(var1))  #no duplicates in list, all elements are now unique
    return len(var2)    #count number of elements = number of unique letters