Please help explaining code

1 2 3 4 def decryption(key, message): message message.upper() alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" result = print(key) for letter in message: if letter in alpha: letter_index - (alpha.find(letter) - key) % len(alpha) 5 6 7 8 9 10 11 result = result + alpha[letter_index] else: result = result + letter return result 12 13 14 15 16 17 18 def main(): filename = "ceaserEncrypted.txt" ceaser_list = [] # file reading with open(filename) as file_in: ceaser_list = [] for line in file_in: ceaser_list.append(line) 19 20 21 22 23 24 25 26 27 decrypted_list = [] # store key key = int(ceaser_list[@]) # decrypt every message for message in ceaser_list[1:]: decrypted decryption(key, message) decrypted_list.append(decrypted) 28 29 = 30 31 32 # make output file filei - open("ceaserDecrypted.txt", "W") 33 34 35 36 # write to output file for mesage in decrypted_list: filel.write(mesage) 37 38 39 40 maino