code: def rectwidth(self, wavelengths=None):
          
          equvw = self.equivwidth(wavelengths=wavelengths)
          tpeak = self.tpeak(wavelengths=wavelengths)
  
          if tpeak.value == 0:  # pragma: no cover
              rectw = 0.0 * self._internal_wave_unit
          else:
              rectw = equvw / tpeak
  
          return rectw
docs: Calculate :ref:`bandpass rectangular width <synphot-formula-rectw>`.
  
          Parameters
          ----------
          wavelengths : array-like, `~astropy.units.quantity.Quantity`, or `None`
              Wavelength values for sampling.
              If not a Quantity, assumed to be in Angstrom.
              If `None`, ``self.waveset`` is used.
  
          Returns
          -------
          rectw : `~astropy.units.quantity.Quantity`
              Bandpass rectangular width.