code: def write_reg(self, filename):
          
          with open(filename, 'w') as out:
              for d in range(1, self.maxdepth+1):
                  for p in self.pixeldict[d]:
                      line = "fk5; polygon("
                      # the following int() gets around some problems with np.int64 that exist prior to numpy v 1.8.1
                      vectors = list(zip(*hp.boundaries(2**d, int(p), step=1, nest=True)))
                      positions = []
                      for sky in self.vec2sky(np.array(vectors), degrees=True):
                          ra, dec = sky
                          pos = SkyCoord(ra/15, dec, unit=(u.degree, u.degree))
                          positions.append(pos.ra.to_string(sep=':', precision=2))
                          positions.append(pos.dec.to_string(sep=':', precision=2))
                      line += ','.join(positions)
                      line += ")"
                      print(line, file=out)
          return
docs: Write a ds9 region file that represents this region as a set of diamonds.
  
          Parameters
          ----------
          filename : str
              File to write