'Mark a function for exporting in the extension module.'

def export(self, exported_name, sig):

    (fn_args, fn_retty) = sigutils.normalize_signature(sig)
    sig = typing.signature(fn_retty, *fn_args)
    if (exported_name in self._exported_functions):
        raise KeyError(('duplicated    export    symbol    %s' % exported_name))
    def decorator(func):
        entry = ExportEntry(exported_name, sig, func)
        self._exported_functions[exported_name] = entry
        return func
    return decorator
