Validates a python format representation of the value.

def Validate(self, value, **_):
    """Validates a python format representation of the value."""
    if isinstance(value, rdfvalue.RDFString):
      # TODO(hanuszczak): Use `str` here.
      return Text(value)

    if isinstance(value, Text):
      return value

    if isinstance(value, bytes):
      return value.decode("utf-8")

    raise type_info.TypeValueError("Not a valid unicode string: %r" % value)