Base85 Encoder / Decoder

import struct

def encode_ascii85(data: bytes) -> str:
    result = []
    for i in range(0, len(data), 4):
        chunk = data[i:i+4]
        padded = chunk.ljust(4, b'\x00')
        n = struct.unpack('>I', padded)[0]
        if n == 0 and len(chunk) == 4:
            result.append('z')
        else:
            chars = []
            for _ in range(5):
                chars.append(chr(n % 85 + 33))
                n //= 85
            result.extend(reversed(chars[:len(chunk)+1]))
    return '<~' + ''.join(result) + '~>'

def decode_ascii85(s: str) -> bytes:
    s = s.strip()
    if s.startswith('<~') and s.endswith('~>'):
        s = s[2:-2]
    result = bytearray()
    i = 0
    while i < len(s):
        if s[i] == 'z':
            result.extend(b'\x00' * 4); i += 1
        else:
            chunk = s[i:i+5]
            n = sum((ord(c) - 33) * (85 ** (4 - j)) for j, c in enumerate(chunk))
            result.extend(struct.pack('>I', n)[:len(chunk)-1])
            i += 5
    return bytes(result)

text = "Hello, World!"
encoded = encode_ascii85(text.encode())
print("Encoded:", encoded)
print("Decoded:", decode_ascii85(encoded).decode())