<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def generateRaDec(self):
 """ Convert XY positions into sky coordinates using STWCS methods. """

        self.prefix = self.PAR_PREFIX

        if not isinstance(self.wcs,pywcs.WCS):
            print(
                textutil.textbox(
                    'WCS not a valid PyWCS object. '
                    'Conversion of RA/Dec not possible...'
                    ),
                file=sys.stderr
            )
            raise ValueError

        if self.xypos is None or len(self.xypos[0]) == 0:
            self.xypos = None
            warnstr = textutil.textbox(
                'WARNING: \n'
                'No objects found for this image...'
            )

            for line in warnstr.split('\n'):
                log.warning(line)

            print(warnstr)
            return

        if self.radec is None:
            print('     Found {:d} objects.'.format(len(self.xypos[0])))
            if self.wcs is not None:
                ra, dec = self.wcs.all_pix2world(self.xypos[0], self.xypos[1], self.origin)
                self.radec = [ra, dec] + copy.deepcopy(self.xypos[2:])
            else:
                # If we have no WCS, simply pass along the XY input positions
                # under the assumption they were already sky positions.
                self.radec = copy.deepcopy(self.xypos)