code: def read(calc_id, username=None):
      
      if isinstance(calc_id, str) or calc_id < 0 and not username:
          # get the last calculation in the datastore of the current user
          return datastore.read(calc_id)
      job = logs.dbcmd('get_job', calc_id, username)
      if job:
          return datastore.read(job.ds_calc_dir + '.hdf5')
      else:
          # calc_id can be present in the datastore and not in the database:
          # this happens if the calculation was run with `oq run`
          return datastore.read(calc_id)
docs: :param calc_id: a calculation ID
      :param username: if given, restrict the search to the user's calculations
      :returns: the associated DataStore instance