code: def write_sparse_matrix_hdf5(filename, mtx, name='a sparse matrix'):
      
      fd = pt.openFile(filename, mode='w', title=name)
      try:
          info = fd.createGroup('/', 'info')
          fd.createArray(info, 'dtype', mtx.dtype.str)
          fd.createArray(info, 'shape', mtx.shape)
          fd.createArray(info, 'format', mtx.format)
  
          data = fd.createGroup('/', 'data')
          fd.createArray(data, 'data', mtx.data)
          fd.createArray(data, 'indptr', mtx.indptr)
          fd.createArray(data, 'indices', mtx.indices)
  
      except:
          print 'matrix must be in SciPy sparse CSR/CSC format!'
          print mtx.__repr__()
          raise
  
      fd.close()
docs: Assume CSR/CSC.