How to use the uharfbuzz.Face.create function in uharfbuzz

self.instance_coordinates = {a.axisTag: a.defaultValue for a in
                                    self._src_ttfont['fvar'].axes}
            for axis in axes:
                if axis in self.instance_coordinates:
                    self.instance_coordinates[axis] = axes[axis]
                else:
                    logger.info("font has no axis called {}".format(axis))
            self.recalc_tables()

            coords = []
            for name in self.axis_order:
                coord = FT_Fixed(int(self.instance_coordinates[name]) << 16)
                coords.append(coord)
            ft_coords = (FT_Fixed * len(coords))(*coords)
            FT_Set_Var_Design_Coordinates(self.ftfont._FT_Face, len(ft_coords), ft_coords)
            self.hbface = hb.Face.create(self._fontdata)
            self.hbfont = hb.Font.create(self.hbface)
            self.hbfont.set_variations(self.instance_coordinates)
            self.hbfont.scale = (self.size, self.size)
        else:
            logger.info("Not vf")

ctx.set_source_rgb(0.5, 0.5, 0.5)
    ctx.move_to(20, 50)
    if title:
        ctx.show_text("{}: {}".format(title, len(diff_table)))
    ctx.move_to(20, 100)
    if font_position:
        ctx.show_text("Font Set: {}".format(font_position))
    if len(diff_table) > item_limit:
        ctx.set_font_size(20)
        ctx.move_to(20, 150)
        ctx.show_text("Warning: {} different items. Only showing most serious {}".format(
            len(diff_table), item_limit)
        )

    # HB font
    hb_face = hb.Face.create(open(font.path, 'rb').read())
    hb_font = hb.Font.create(hb_face)
    hb_upem = upm_size

    hb_font.scale = (hb_upem, hb_upem)
    if font.is_variable:
        hb_font.set_variations(font.axis_locations)
    hb.ot_font_set_funcs(hb_font)

    # Draw glyphs
    x, y, baseline = 20, 200, 0
    x_pos = 20
    y_pos = 200
    for row in diff_table[:item_limit]:

        buf = hb.Buffer.create()
        buf.add_str(row['string'])

self.axis_order = None
        self.instance_coordinates = self._get_dflt_instance_coordinates()
        self.instances_coordinates = self._get_instances_coordinates()
        self.glyphs = self.marks = self.mkmks = self.kerns = \
            self.glyph_metrics = self.names = self.attribs = None

        self.ftfont = freetype.Face(self.path)
        self.ftslot = self.ftfont.glyph

        self.size = size
        if self.ftfont.is_scalable:
            self.ftfont.set_char_size(self.size)

        with open(self.path, 'rb') as fontfile:
            self._fontdata = fontfile.read()
        self.hbface = hb.Face.create(self._fontdata)
        self.hbfont = hb.Font.create(self.hbface)

        self.hbfont.scale = (self.size, self.size)

        if not lazy:
            self.recalc_tables()