Sets a CSS stylesheet. The classes in the stylesheet should
        correspond to those generated by:
            pygmentize -S <style> -f html
        Note that 'set_style' and 'set_style_sheet' completely override each
        other, i.e. they cannot be used in conjunction.

def set_style_sheet(self, stylesheet):
        """ Sets a CSS stylesheet. The classes in the stylesheet should
        correspond to those generated by:
            pygmentize -S <style> -f html
        Note that 'set_style' and 'set_style_sheet' completely override each
        other, i.e. they cannot be used in conjunction.
        """
        self._document.setDefaultStyleSheet(stylesheet)
        self._style = None
        self._clear_caches()