<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def decode(byte_str, allow_none=False):
 """Make this unicode in Python 3, otherwise leave it as bytes. Args: byte_str: The byte string to decode. allow_none: If true, then we will allow byte_str to be None in which case we will return an empty string. TODO(rkn):
 Remove this flag. This is only here to simplify upgrading to flatbuffers 1.10.0. Returns: A byte string in Python 2 and a unicode string in Python 3. """

    if byte_str is None and allow_none:
        return ""

    if not isinstance(byte_str, bytes):
        raise ValueError(
            "The argument {} must be a bytes object.".format(byte_str))
    if sys.version_info >= (3, 0):
        return byte_str.decode("ascii")
    else:
        return byte_str