alphabet = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z']

file = 'target.txt'
method = 2
newlines = []
read = open(file, 'r')
lines = read.readlines()
read.close()
for line in lines:
    new_line = ""
    for letter in line:
        if letter.upper() not in alphabet:
            new_line += letter
        else:
            new_letter = alphabet.index(letter.upper())+method
            while new_letter > len(alphabet)-1:
                new_letter -= len(alphabet)
            else:
                nl = alphabet[new_letter]
                if letter.islower() == True:
                    new_line += nl.lower()
                else:
                    new_line += nl
    newlines.append(new_line)
file_handle = open(file, 'w')
for line in newlines:
    file_handle.write(line)
file_handle.close()
print("The file {} has been encrypted!".format(file))