I'm a relatively new programmer. I've made a simple Vigenere cipher program. It takes three arguments and acts on a file. I have made some of the steps more "explict" for myself by using more lists than I need to, rather than applying multiple "transformations" at a time. I would appreciate feedback on how this code would be written differently by people who know more than I do.
#!/usr/bin/env python3
# vigenere.py - This program has two modes, encrypt and decrypt. It takes
# three arguments: the mode('encrypt' or 'decrypt'), a keyword, and a
# filename to act upon. It is designed to work with lowercase letters.
from sys import argv
from itertools import cycle
# User specifies a mode, a key, and a file with argv arguments
def start():
if len(argv) > 1:
mode = argv[1]
key = argv[2]
plaintextFilename = argv[3]
else:
print('Please supply mode, key, and file as arguments.')
exit()
# Start the mode selected
if mode == 'encrypt':
encryptMode()
elif mode == 'decrypt':
decryptMode()
else:
print('Please supply \'encrypt\' or \'decrypt\' mode.')
exit()
# Encryption Mode
def encryptMode():
# Open the alpha plaintext file as an object
alphaPlaintextFileObj = open(argv[3])
# Create the ordinal plaintext data structure
ordinalPlaintext = []
# Populate the ordinal plaintext data structure
for c in alphaPlaintextFileObj.read():
if c == ' ':
ordinalPlaintext.append(' ')
else:
o = ord(c) - 65
ordinalPlaintext.append(o)
# Create an ordinal ciphertext data structure
ordinalCiphertext = []
# Turn the key into an ordinal key where a = 1, etc.
ordinalKey = []
key = argv[2]
for c in key:
n = ord(c) - 96
ordinalKey.append(n)
# Populate the ordinalCiphertext structure with numbers shifted using the
# ordinal key.
for k, p in zip(cycle(ordinalKey), ordinalPlaintext):
if p == ' ':
ordinalCiphertext.append(' ')
else:
c = (k + p) % 25
ordinalCiphertext.append(c)
# Create the alpha ciphertext file
alphaCiphertextFilename = argv[3] + '_encrypted'
alphaCiphertextFileObj = open(alphaCiphertextFilename, 'w')
# Populate the alpha ciphertext file
for c in ordinalCiphertext:
if c == ' ':
alphaCiphertextFileObj.write(' ')
else:
l = chr(int(c) + 65)
alphaCiphertextFileObj.write(l)
# Save and close the plaintext and ciphertext files.
alphaPlaintextFileObj.close()
alphaCiphertextFileObj.close()
# Print a message telling the user the operation is complete.
print(f'{argv[3]} encrypted as {alphaCiphertextFilename}')
# Decryption Mode
def decryptMode():
# Open the alpha ciphertext file as an object
alphaCiphertextFileObj = open(argv[3])
# Create the ordinal ciphertext data structure
ordinalCiphertext = []
# Populate the ordinal ciphertext data structure
for c in alphaCiphertextFileObj.read():
if c == ' ':
ordinalCiphertext.append(' ')
else:
o = ord(c) - 97
ordinalCiphertext.append(o)
# Create the ordinal key
ordinalKey = []
key = argv[2]
for c in key:
n = ord(c) - 96
ordinalKey.append(n)
#Create the ordinal plaintext data structure
ordinalPlaintext = []
# Populate the ordinal plaintext data structure with the modular
# difference of the ordinal ciphertext and the ordinal key
for k, c in zip(cycle(ordinalKey), ordinalCiphertext):
if c == ' ':
ordinalPlaintext.append(' ')
else:
p = (c - k) % 25
ordinalPlaintext.append(p)
# Create the alpha plaintext file
alphaPlaintextFilename = argv[3] + '_decrypted'
alphaPlaintextFileObj = open(alphaPlaintextFilename, 'w')
# Convert the ordinal plaintext to an alpha plaintext file,
# 'filename_decrypted'
for p in ordinalPlaintext:
if p == ' ':
alphaPlaintextFileObj.write(' ')
else:
l = chr(int(p) + 97)
alphaPlaintextFileObj.write(l)
# Save and close the ciphertext and plaintext files
alphaCiphertextFileObj.close()
alphaPlaintextFileObj.close()
# Print a message telling the user the operation is complete
print(f'{argv[3]} decrypted as {alphaPlaintextFilename}')
start()
