发生异常时，我应该提出还是冒犯？

Question

I'm implementing endpoint at tornado app and have doubts how to raise and handle exceptions.

I have get method which collects all raised exceptions and logs them. It looks like this:

def get(self):
    try:
        req = self.get_request_params()
    except Exception as e:
        self.send_json(status_code=400, status_text=str(e))
        logging.exception(str(e))

And here is get_request_params which might throw an exception:

def get_request_params(self):
    try:
        user_id = UUID(self.get_query_argument("user_id", None))
    except ValueError:
        raise ValueError("Incorrect argument value for user_id = %s" % user_id)

    try:
        from_date = self.get_query_argument("from", default=None)
        datetime.datetime.strptime(from_date, '%Y-%m-%d')
    except ValueError:
        raise ValueError("Incorrect argument value for from_date = %s, should be YYYY-MM-DD" % from_date)
    ...

There are also other request params, which checked in the same way. Looks like I'm trying to do more than necessary. Instead of it I can have something like this:

def get_request_params(self):
    user_id = UUID(self.get_query_argument("user_id", None))
    from_date = self.get_query_argument("from", default=None)
    datetime.datetime.strptime(from_date, '%Y-%m-%d')
    ...

In such case any exception will bubble up and will be handled at get method. However, I will lost those pretty messages.

So, should I be so explicit in raising exceptions or it's enough to permit thing go as they are?

Answer 1

If you catch an exception, it means you intend to do something about it, even if that something is just output a custom logging message before ignoring it or re-raising it. If the only thing you do is re-raise it, then you shouldn't have caught it in the first place. (This might indicate that the class of error you are catching is too broad.)