code: def save_vlen(self, key, data):
          
          shape = (None,) + data[0].shape[:-1]
          try:
              dset = self[key]
          except KeyError:
              vdt = h5py.special_dtype(vlen=data[0].dtype)
              dset = create(self, key, vdt, shape, fillvalue=None)
          nbytes = dset.attrs.get('nbytes', 0)
          totlen = dset.attrs.get('totlen', 0)
          for i, val in enumerate(data):
              nbytes += val.nbytes
              totlen += len(val)
          length = len(dset)
          dset.resize((length + len(data),) + shape[1:])
          for i, arr in enumerate(data):
              dset[length + i] = arr
          dset.attrs['nbytes'] = nbytes
          dset.attrs['totlen'] = totlen
docs: Save a sequence of variable-length arrays
  
          :param key: name of the dataset
          :param data: data to store as a list of arrays