code: def _slow_calcbinflux(len_binwave, i_beg, i_end, avflux, deltaw):
      
      binflux = np.empty(shape=(len_binwave, ), dtype=np.float64)
      intwave = np.empty(shape=(len_binwave, ), dtype=np.float64)
  
      # Note that, like all Python striding, the range over which
      # we integrate is [first:last).
      for i in range(len(i_beg)):
          first = i_beg[i]
          last = i_end[i]
          cur_dw = deltaw[first:last]
          intwave[i] = cur_dw.sum()
          binflux[i] = np.sum(avflux[first:last] * cur_dw) / intwave[i]
  
      return binflux, intwave
docs: Python implementation of ``calcbinflux``.
  
      This is only used if ``synphot.synphot_utils`` C-extension
      import fails.
  
      See docstrings.py