def get_design_loc(self, glyphs_master_or_instance):
return getattr(glyphs_master_or_instance, self.design_loc_key)<EOL>
Get the design location (aka interpolation value) of a Glyphs
        master or instance along this axis. For example for the weight
        axis it could be the thickness of a stem, for the width a percentage
        of extension with respect to the normal width.