pack.py 文件源码

def split_field(byte_len, data_bytes):
    '''
    Return a tuple containing the first byte_len bytes in data_bytes, and the
    remainder of data_bytes.
    Asserts if data_bytes is not at least byte_len bytes long.
    '''
    assert len(data_bytes) >= byte_len
    return (bytearray(data_bytes[0:byte_len]),
            bytearray(data_bytes[byte_len:]))

# struct formats. See
# https://docs.python.org/2/library/struct.html#byte-order-size-and-alignment