How to Create an Encryption Program with Python

from Crypto.Hash import SHA256
from Crypto.Cipher import AES
import os, random, sys, pkg_resources

def encrypt(key, filename):
    chunksize = 64 * 1024
    outFile = os.path.join(os.path.dirname(filename), "(encrypted)"+os.path.basename(filename))
    filesize = str(os.path.getsize(filename)).zfill(16)
    IV = ''

    for i in range(16):
        IV += chr(random.randint(0, 0xFF))

    encryptor = AES.new(key, AES.MODE_CBC, IV)

    with open(filename, "rb") as infile:
        with open(outFile, "wb") as outfile:
            outfile.write(filesize)
            outfile.write(IV)
            while True:
                chunk = infile.read(chunksize)

                if len(chunk) == 0:
                    break

                elif len(chunk) % 16 !=0:
                    chunk += ' ' *  (16 - (len(chunk) % 16))

                outfile.write(encryptor.encrypt(chunk))


def decrypt(key, filename):
    outFile = os.path.join(os.path.dirname(filename), os.path.basename(filename[11:]))
    chunksize = 64 * 1024
    with open(filename, "rb") as infile:
        filesize = infile.read(16)
        IV = infile.read(16)

        decryptor = AES.new(key, AES.MODE_CBC, IV)

        with open(outFile, "wb") as outfile:
            while True:
                chunk = infile.read(chunksize)
                if len(chunk) == 0:
                    break

                outfile.write(decryptor.decrypt(chunk))

            outfile.truncate(int(filesize))

def allfiles():
    allFiles = []
    for root, subfiles, files in os.walk(os.getcwd()):
        for names in files:
            allFiles.append(os.path.join(root, names))

    return allFiles


choice = raw_input("Do you want to (E)ncrypt or (D)ecrypt? ")
password = raw_input("Enter the password: ")

encFiles = allfiles()

if choice == "E":
    for Tfiles in encFiles:
        if os.path.basename(Tfiles).startswith("(encrypted)"):
            print "%s is already encrypted" %str(Tfiles)
            pass

        elif Tfiles == os.path.join(os.getcwd(), sys.argv[0]):
            pass
        else:
            encrypt(SHA256.new(password).digest(), str(Tfiles))
            print "Done encrypting %s" %str(Tfiles)
            os.remove(Tfiles)


elif choice == "D":
    filename = raw_input("Enter the filename to decrypt: ")
    if not os.path.exists(filename):
        print "The file does not exist"
        sys.exit(0)
    elif not filename.startswith("(encrypted)"):
        print "%s is already not encrypted" %filename
        sys.exit()
    else:
        decrypt(SHA256.new(password).digest(), filename)
        print "Done decrypting %s" %filename
        os.remove(filename)

else:
    print "Please choose a valid command."
    sys.exit()