根据spec来生成handler函数参数值读取器

def argument_getter_factory(route_spec):
    """ 根据spec来生成handler函数参数值读取器 """ 
    
    func_sig = inspect.signature(route_spec.handler_func)

    param_names = list(func_sig.parameters.keys())
    arg_getters  = build_argval_getters(route_spec)
    n_args = len(arg_getters)

    async def argument_getters(request):
        errors = None
        values = {}
        for i in range(n_args):
            try:
                arg_name = param_names[i]
                values[arg_name] = await arg_getters[i](request)
            except HTTPException:
                raise
            except Exception as exc :
                if errors is None: 
                    errors = []

                request.app.logger.error('', exc_info=True)

                exc_type = type(exc)

                data = {
                    "name": arg_name, 
                    "type": f"{exc_type.__module__}.{exc_type.__qualname__}",
                    "error": str(exc)
                }

                errors.append(data)

        if errors is not None:
            raise RESTfulArgumentError(errors)

        return values

    return argument_getters