code: def _uniq(self):
          
          pd = []
          for d in range(1, self.maxdepth):
              pd.extend(map(lambda x: int(4**(d+1) + x), self.pixeldict[d]))
          return sorted(pd)
docs: Create a list of all the pixels that cover this region.
          This list contains overlapping pixels of different orders.
  
          Returns
          -------
          pix : list
              A list of HEALPix pixel numbers.