base64.py 文件源码

def _85encode(b, chars, chars2, pad=False, foldnuls=False, foldspaces=False):
    # Helper function for a85encode and b85encode
    if not isinstance(b, bytes_types):
        b = memoryview(b).tobytes()

    padding = (-len(b)) % 4
    if padding:
        b = b + b'\0' * padding
    words = struct.Struct('!%dI' % (len(b) // 4)).unpack(b)

    chunks = [b'z' if foldnuls and not word else
              b'y' if foldspaces and word == 0x20202020 else
              (chars2[word // 614125] +
               chars2[word // 85 % 7225] +
               chars[word % 85])
              for word in words]

    if padding and not pad:
        if chunks[-1] == b'z':
            chunks[-1] = chars[0] * 5
        chunks[-1] = chunks[-1][:-padding]

    return b''.join(chunks)