code: def write_strain(self, strain_dict, group=None):
          
          subgroup = self.data_group + "/{ifo}/strain"
          if group is None:
              group = subgroup
          else:
              group = '/'.join([group, subgroup])
          for ifo, strain in strain_dict.items():
              self[group.format(ifo=ifo)] = strain
              self[group.format(ifo=ifo)].attrs['delta_t'] = strain.delta_t
              self[group.format(ifo=ifo)].attrs['start_time'] = \
                  float(strain.start_time)
docs: Writes strain for each IFO to file.
  
          Parameters
          -----------
          strain : {dict, FrequencySeries}
              A dict of FrequencySeries where the key is the IFO.
          group : {None, str}
              The group to write the strain to. If None, will write to the top
              level.