convert Flipnote Studio .lst and .pls files to and from .txt

lst.py

from sys import argv
import hashlib
import numpy as np

xorkey = [
    0xF7, 0x4C, 0x6A, 0x3A, 0xFB, 0x82, 0xA6, 0x37,
    0x6E, 0x11, 0x38, 0xCF, 0xA0, 0xDD, 0x85, 0xC0,
    0xC7, 0x9B, 0xC4, 0xD8, 0xDD, 0x28, 0x8A, 0x87,
    0x53, 0x20, 0xEE, 0xE0, 0x0B, 0xEB, 0x43, 0xA0,
    0xDB, 0x55, 0x0F, 0x75, 0x36, 0x37, 0xEB, 0x35,
    0x6A, 0x34, 0x7F, 0xB5, 0x0F, 0x99, 0xF7, 0xEF,
    0x43, 0x25, 0xCE, 0xA0, 0x29, 0x46, 0xD9, 0xD4,
    0x4D, 0xBB, 0x04, 0x66, 0x68, 0x08, 0xF1, 0xF8
]

def xor(data):
    # Storage for the decrypted entry data
    decrypted = bytes();
    # XOR the entry data
    for index, byte in enumerate(data):
        decrypted += bytes([ byte ^ xorkey[index % len(xorkey)] ]);
    # Convert the XOR'ed data to a bytes object
    return decrypted

def checksum(data):
    hash = hashlib.md5()
    hash.update(data)
    digest = hash.digest()
    return bytes([digest[6], digest[8]])

def decode(lstBuffer, outBuffer):
    data = lstBuffer.read()
    xordata = xor(data)
    # Find the first null byte in the decoded file -- this is where the entry content ends
    entryLength = xordata.index(b"\x00") + 1
    # Write the entry data to the out buffer, removing the final newline and the null byte at the end
    outBuffer.write(xordata.split(b"\x0A\x00")[0])

def encode(txtBuffer, outBuffer, targetLength):
    # Split the xtx file buffer into lines
    content = txtBuffer.readlines()
    # Strip any newlines that are left
    content = [x.strip("\n") for x in content]
    # Join all the items in content together with newlines between
    # (We do all this just to make sure the input is "clean")
    content = "\n".join(content)
    # Create a bytearray and add the content to it
    data = bytearray()
    data.extend(map(ord, content))
    # Add the trailing newline and null byte
    data += bytes([0x0A, 0x00])
    # Checksum everything
    md5 = checksum(data)
    # XOR all the data so far
    data = xor(data)
    # Add a checksum to the XOR data
    data += md5
    # Load the data into a numpy array
    data = np.fromstring(data, dtype=np.uint8)
    # Add null padding
    data = np.pad(data, (0, targetLength - len(data)), 'constant', constant_values=(0, 0))
    # Convert the array to bytes and write them to the out buffer
    outBuffer.write(data.tobytes())

if len(argv) < 3:
    print("\nlst.py")
    print("writen by james daniel (github.com/jaames)")
    print("\nconvert .txt to .lst/.pls:")
    print("\tpython3 lst.py -e input.txt output.lst desired_length_in_bytes")
    print("\n\tlength reference:")
    print("\t.dirmemo2.lst - 160000")
    print("\t.mark0.pls | mark1.pls | mark2.pls | mark3.pls - 8000")
    print("\t.recent10.pls - 4000")
    print("\nconvert .lst/.pls to .txt:")
    print("\tpython3 lst.py -d input.lst output.txt")

else:
    if argv[1] == "-e":
        with open(argv[2], "r") as txt, open(argv[3], "wb") as lst:
            encode(txt, lst, int(argv[4]))
    elif args[1] == "-d":
        with open(argv[2], "rb") as lst, open(argv[3], "wb") as txt:
            decode(lst, txt)

I think you have a typo on line 81, "args" instead of "argv"