<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _unpack_oxm_field(self):
 """Unpack oxm_field from oxm_field_and_mask. Returns: :class:`OxmOfbMatchField`, int: oxm_field from oxm_field_and_mask. Raises: ValueError: If oxm_class is OFPXMC_OPENFLOW_BASIC but :class:`OxmOfbMatchField` has no such integer value. """

        field_int = self.oxm_field_and_mask >> 1
        # We know that the class below requires a subset of the ofb enum
        if self.oxm_class == OxmClass.OFPXMC_OPENFLOW_BASIC:
            return OxmOfbMatchField(field_int)
        return field_int