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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def to_fits(self, filename, wavelengths=None, **kwargs):
 """Write the reddening law to a FITS file. :math:`R(V)` column is automatically named 'Av/E(B-V)'. Parameters filename : str Output filename. 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. kwargs : dict Keywords accepted by :func:`~synphot.specio.write_fits_spec`. """

        w, y = self._get_arrays(wavelengths)

        kwargs['flux_col'] = 'Av/E(B-V)'
        kwargs['flux_unit'] = self._internal_flux_unit

        # No need to trim/pad zeroes, unless user chooses to do so.
        if 'pad_zero_ends' not in kwargs:
            kwargs['pad_zero_ends'] = False
        if 'trim_zero' not in kwargs:
            kwargs['trim_zero'] = False

        # There are some standard keywords that should be added
        # to the extension header.
        bkeys = {'tdisp1': 'G15.7', 'tdisp2': 'G15.7'}

        if 'expr' in self.meta:
            bkeys['expr'] = (self.meta['expr'], 'synphot expression')

        if 'ext_header' in kwargs:
            kwargs['ext_header'].update(bkeys)
        else:
            kwargs['ext_header'] = bkeys

        specio.write_fits_spec(filename, w, y, **kwargs)