code: def iter_regions(self):
          
          # TODO: Implement BoundingBox
          # TODO: Implement sort order
          for x,z in self.regionfiles.keys():
              close_after_use = False
              if (x,z) in self.regions:
                  regionfile = self.regions[(x,z)]
              else:
                  # It is not yet cached.
                  # Get file, but do not cache later.
                  regionfile = region.RegionFile(self.regionfiles[(x,z)], chunkclass = self.chunkclass)
                  regionfile.loc = Location(x=x,z=z)
                  close_after_use = True
              try:
                  yield regionfile
              finally:
                  if close_after_use:
                      regionfile.close()
docs: Return an iterable list of all region files. Use this function if you only
          want to loop through each region files once, and do not want to cache the results.