code: def to_hdf(self,path,key,mode='a'):
          
          pd.DataFrame(self.serialize()).to_hdf(path,key,mode=mode,format='table',complib='zlib',complevel=9)
          f = h5py.File(path,'r+')
          f[key].attrs["microns_per_pixel"] = float(self.microns_per_pixel) if self.microns_per_pixel is not None else np.nan
          f.close()
docs: Save the CellDataFrame to an hdf5 file.
  
          Args:
              path (str): the path to save to
              key (str): the name of the location to save it to
              mode (str): write mode