name_game.py

# Get a list of names
def get_name_list():
    name_list = []
    name = input("Enter name #1 (or press enter to stop): ")
    # Keep going until the empty string is returned by input.
    while name != "":
        # Append the most recent name and ask the user for the next name.
        name_list.append(name.upper())
        name = input("Enter name #"+str(len(name_list)+1)+" (or press enter to stop): ")

    return name_list


# Returns a set of letters that are missing from all strings in name_list
def get_missing_letters(name_list):
    missing_letters = set('ABCDEFGHIJKLMNOPQRSTUVWXYZ')
    once_letters = set()

    #print(missing_letters)
    #print(once_letters)
    #print("-------------------------")

    for name in name_list:
        # Get first and second time letters
        name_letters = set(name)
        first_time_letters = missing_letters & name_letters
        second_time_letters = once_letters & name_letters

        # Update missing and once letter sets.
        missing_letters -= first_time_letters
        once_letters = (once_letters | first_time_letters) - second_time_letters

        #print(missing_letters)
        #print(once_letters)
        #print("-------------------------")

    return missing_letters, once_letters


# The main function
def main():
    # Get the list of first names
    name_list = get_name_list()

    # Get letters that appear in NO names
    missing_letter_set, once_letter_set = get_missing_letters(name_list)

    missing_letters = list(missing_letter_set)
    missing_letters.sort()
    print("Missing letters are: ", missing_letters)

    once_letters = list(once_letter_set)
    once_letters.sort()
    print("Seen once letters are: ", once_letters)

# Run the program
main()