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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 from_file(cls, filename, beam=None):
 """ 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 """

        header = fits.getheader(filename)
        return cls.from_header(header, beam)