base64.py

class Base64:
    import string
    import binascii

    def __init__(self):
        b64chars = (
            string.ascii_uppercase + string.ascii_lowercase + string.digits + "+/"
        )
        self.c2i = {c: i for i, c in enumerate(b64chars)}
        self.c2i["="] = 0
        self.i2c = {i: c for i, c in enumerate(b64chars)}

    def decode(self, b64str):
        bit_str = "".join([f"{self.c2i[c]:06b}" for c in b64str])
        decoded = [chr(int(b, 2)) for b in into_chunk(bit_str, 8)]
        decoded = "".join([c for c in decoded if c != "\x00"])
        return decoded

    def encode(self, ascii_str):
        bit_str = "".join([f"{ord(b):08b}" for b in ascii_str])
        pad = -len(bit_str) % 6
        bit_str += "0" * pad
        encoded = [self.i2c[int(b, 2)] for b in into_chunk(bit_str, 6)]
        encoded = "".join(encoded)
        pad = -len(encoded) % 4
        encoded += "=" * pad
        return encoded

    @classmethod
    def into_chunk(bit_str, chunk_size):
        return [bit_str[i : i + chunk_size] for i in range(0, len(bit_str), chunk_size)]