How to handle missing parameters in URL with Flask/Python 3 [duplicate]

Question

Currently, my website has two drop down boxes on it whose values, upon form submission, translate to two URL parameters "myState" and "myShelter". For example:

https://www.atweather.org/forecast?myState=CT&myShelter=181

I'm now adding a third box and there will be a third corresponding parameter called "myTrail". My question is this: how can I make it so that if someone directly submits a URL with just the two parameters, the browser will not error out with a bad request? I would want the user to see the page as though "myState" and "myShelter" were picked, but "myTrail" was just left unselected.

I tried looking here and here, but I don't think these are quite the same situation as what I'm asking about. I'm using Flask under Python 3 and currently handle this route like so:

@app.route('/forecast', methods = ['GET'])
def forecast(loc_state = None, loc_id = None):

    """
    Handles rendering of page after a location has been selected
    """

    loc_state = request.args['myState']
    loc_id = int(request.args['myShelter'])

    ...and a bunch of other logic for rendering the page...

Thanks in advance for any insight!

iurisilvio · Accepted Answer · 2016-05-02 16:43:20Z

4

The request.args.get() method allows to get the argument if it exists.

# return None if the argument doesn't exist
trail = request.args.get('myTrail')

# return 'x' if the argument doesn't exist
trail = request.args.get('myTrail', 'x')

After this, just handle the value to return the way you want.

answered May 2, 2016 at 16:43

iurisilvio

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