code: def binned_waverange(self, cenwave, npix, **kwargs):
          
          # Calculation is done in the unit of cenwave.
          if not isinstance(cenwave, u.Quantity):
              cenwave = cenwave * self._internal_wave_unit
  
          bin_wave = units.validate_quantity(
              self.binset, cenwave.unit, equivalencies=u.spectral())
  
          return binning.wave_range(
              bin_wave.value, cenwave.value, npix, **kwargs) * cenwave.unit
docs: Calculate the wavelength range covered by the given number
          of pixels centered on the given central wavelengths of
          `binset`.
  
          Parameters
          ----------
          cenwave : float or `~astropy.units.quantity.Quantity`
              Desired central wavelength.
              If not a Quantity, assumed to be in Angstrom.
  
          npix : int
              Desired number of pixels, centered on ``cenwave``.
  
          kwargs : dict
              Keywords accepted by :func:`synphot.binning.wave_range`.
  
          Returns
          -------
          waverange : `~astropy.units.quantity.Quantity`
              Lower and upper limits of the wavelength range,
              in the unit of ``cenwave``.