Encode binary data into uppercase-only ASCII

ascii_upper_encoder.py

ASCII_A_CODE = ord('A')

def ascii_upper_encode(data):
    code = ''
    for byte in data:
        code += chr((byte >> 4) + ASCII_A_CODE)
        code += chr((byte & 0xf) + ASCII_A_CODE)
    return code

def ascii_upper_decode(code):
    code_size = len(code)
    assert code_size % 2 == 0
    i = 0
    data = b''
    while i < code_size:
        character0 = code[i]
        character1 = code[i + 1]
        assert 'A' <= character0 <= 'P'
        assert 'A' <= character1 <= 'P'
        data += bytes([((ord(character1) - ASCII_A_CODE) & 0xf) | ((ord(character0) - ASCII_A_CODE) << 4)])
        i += 2
    return data