code: def from_file(cls, filename, **kwargs):
          
          if 'flux_unit' not in kwargs:
              kwargs['flux_unit'] = cls._internal_flux_unit
  
          if ((filename.endswith('fits') or filename.endswith('fit')) and
                  'flux_col' not in kwargs):
              kwargs['flux_col'] = 'Av/E(B-V)'
  
          header, wavelengths, rvs = specio.read_spec(filename, **kwargs)
  
          return cls(Empirical1D, points=wavelengths, lookup_table=rvs,
                     meta={'header': header})
docs: Create a reddening law from file.
  
          If filename has 'fits' or 'fit' suffix, it is read as FITS.
          Otherwise, it is read as ASCII.
  
          Parameters
          ----------
          filename : str
              Reddening law filename.
  
          kwargs : dict
              Keywords acceptable by
              :func:`~synphot.specio.read_fits_spec` (if FITS) or
              :func:`~synphot.specio.read_ascii_spec` (if ASCII).
  
          Returns
          -------
          redlaw : `ReddeningLaw`
              Empirical reddening law.