code: def from_file(cls, filename, beam=None):
          
          header = fits.getheader(filename)
          return cls.from_header(header, beam)
docs: Create a new WCSHelper class from a given fits file.
  
          Parameters
          ----------
          filename : string
              The file to be read
  
          beam : :class:`AegeanTools.fits_image.Beam` or None
              The synthesized beam. If the supplied beam is None then one is constructed form the header.
  
          Returns
          -------
          obj : :class:`AegeanTools.wcs_helpers.WCSHelper`
              A helper object