Flask handling multiple errors

May 26, 2022

I have a simple app made in Flask. It uses only POST method.
It takes 2 numbers (in json) and adds them up.

{"a": 1, "b": 1}

The application responds with the sum of these numbers (also in json).

{"sum": 2}

The code looks like this:

@appFlask.route('sum', methods=['POST'])
def result():
    data = request.get_json()
    return jsonify({'sum': data['a'] + data['b']})

I would like to do error handling. The problem is that there are a lot of these errors, e.g. for the following calls, they should return "400 Bad Request" or if the file isn’t in json.

{"a":1, "b":1, "c":1}
{"a", "a":1, "b":1}
{}
{"a":1}
{"a":0, "b":1}

How can i make it in the simplest way? Is there a way to do this in one function?

>Solution :

You can use catch the error and then you can return "400 Bad Request" and return an example of data and it’s validations to the user.

@appFlask.route('sum', methods=['POST'])
def result():
    try:
       data = request.get_json()
       # check if a or b is not 0
       if data['a'] == 0 or data['b'] == 0:
           raise Exception("Error occurred")
       return jsonify({'sum': data['a'] + data['b']})
    except Exception as e:
       return "400 Bad Request"

All the other calls mentioned in example will generate error which will be cached.

You don’t need to worry for {"a":1, "b":1, "c":1} as it will not affect the code but if you want to consider it bad request you need to do a check for it.

You surely need to do checks according to your needs as there is no built in function for that.