'Return a DiskType object from the JSON-response dictionary.
:param  disktype: The dictionary describing the disktype.
:type   disktype: ``dict``
:return: DiskType object
:rtype: :class:`GCEDiskType`'

def _to_disktype(self, disktype):

    extra = {}
    zone = self.ex_get_zone(disktype['zone'])
    extra['selfLink'] = disktype.get('selfLink')
    extra['creationTimestamp'] = disktype.get('creationTimestamp')
    extra['description'] = disktype.get('description')
    extra['valid_disk_size'] = disktype.get('validDiskSize')
    extra['default_disk_size_gb'] = disktype.get('defaultDiskSizeGb')
    type_id = ('%s:%s' % (zone.name, disktype['name']))
    return GCEDiskType(id=type_id, name=disktype['name'], zone=zone, driver=self, extra=extra)
