談到單一責任的時候，有一種常常被忽略的責任就是參數檢查跟消毒(Sanitizer)

一般來說這種東西都會寫成像下面這樣

class TaskListA(Resource):

    def get(self):
        parser = reqparse.RequestParser()
        parser.add_argument('page', type=int, location='args', default=1)
        parser.add_argument('size', type=int, location='args', default=15)
        parser.add_argument('project_id', type=int, location='args', default=0)
        params = parser.parse_args()
        max_size = 150
        status = 200
        size = params['size']
        page = params['page']
        task_status = params['task_status']
        project_id = params['project_id']
        if page <= 0 or size <= 0 or size > max_size:
            status = 400

這邊有個很大的問題，如果今天有十種TaskListB .... TaskListZ

那這段邏輯就會重寫十次，極度恐怖而且極度麻煩

這邊Demo在另外一個專案使用的 sanitizer

decorator.py

def sanitize_parameter(parameter_keys):
    def decorator(func):
        def wrapper(params):
            params_content = []
            for key in parameter_keys:
                if key not in params:
                    raise ParameterNotExist(key)
                value = params.get(key)
                if key == 'ProjectId':
                    project_id = params.get(key)
                    project = mysql.get_project_by_id(project_id)
                    if project is None:
                        raise ProjectNotFound(project_id)
                if key == 'DefaultMode':
                    if not hasattr(TAGGING_MODE, value):
                        raise InvalidDefaultMode(value)
                params_content.append(value)
            return func(*params_content)
        return wrapper
    return decorator

request.py

@http_request
@need_auth
@sanitize_parameter(['ProjectId', 'Keys'])
def import_folder_hits(project_id, keys):
    pass

這樣就能讓變數檢查變成可複製，可重複使用的