Python/ciphers/transposition_cipher_encrypt_decrypt_file.py

import time, os, sys
import transposition_cipher as transCipher


def main():
    inputFile = "Prehistoric Men.txt"
    outputFile = "Output.txt"
    key = int(input("Enter key: "))
    mode = input("Encrypt/Decrypt [e/d]: ")

    if not os.path.exists(inputFile):
        print("File %s does not exist. Quitting..." % inputFile)
        sys.exit()
    if os.path.exists(outputFile):
        print("Overwrite %s? [y/n]" % outputFile)
        response = input("> ")
        if not response.lower().startswith("y"):
            sys.exit()

    startTime = time.time()
    if mode.lower().startswith("e"):
        with open(inputFile) as f:
            content = f.read()
        translated = transCipher.encryptMessage(key, content)
    elif mode.lower().startswith("d"):
        with open(outputFile) as f:
            content = f.read()
        translated = transCipher.decryptMessage(key, content)

    with open(outputFile, "w") as outputObj:
        outputObj.write(translated)

    totalTime = round(time.time() - startTime, 2)
    print(("Done (", totalTime, "seconds )"))


if __name__ == "__main__":
    main()