Passing a date as a URL parameter to a flask route

Question

I want to filter some database results, for a given url with some date parameter (like this url.com?start=2018-12-12). The normal way to read a parameter is with request.args.get, accessing the value of the underlying ImmutableMultiDict, which gives me the optional arguments default and type.

My first attempt now was this:

@app.route()
def event():
   ektempo = request.args.get('start', default = datetime.date.today(), type = datetime.date)
   ...

Which works for the default parameter, but not for the passed date string, since datetime.date needs three integers as parameters. Normally I would get my date object by datetime.datetime.strptime and a format string. Is there a way to pass a datetime string as a url parameter to flask and cast it pythonicly to datetime.date.

I like the way request.args.get works, but it seems I can not get a datetime.date object from it easily with a given url parameter. Is there another way to acheive it by flask bult-in methods, which verifies the parameter and on no parameter or ValueError gives me the default?

Answer 1

As pointed out by Daniel Roseman, you can pass any function to type, so I just defined a little helper function to do the conversion of the date-string and here is it:

def toDate(dateString): 
    return datetime.datetime.strptime(dateString, "%Y-%m-%d").date()

@app.route()
def event():
    ektempo = request.args.get('start', default = datetime.date.today(), type = toDate)
    ...

Yeah, very cool, thanks a lot Daniel, just what I searched for! :)

Answer 2

The accepted solution does the work for the use case (and got my upvote :); yet if the parameter doesn't conform to the expected format, it will set it to the default value (today) silently, with no feedback to the caller - as this is flask's/werkzeug's intended behavior.

Here's how to use it to validate & return an error if the client has passed an invalid value - piggybacking on OP's solution:

from flask import jsonify

def to_date(date_string): 
    try:
        return datetime.datetime.strptime(date_string, "%Y-%m-%d").date()
    except ValueError:
        raise ValueError('{} is not valid date in the format YYYY-MM-DD'.format(date_string))

@app.route()
def event():
    try:
        ektempo = to_date(request.args.get('start', default = datetime.date.today().isoformat()))
    except ValueError as ex:
        return jsonify({'error': str(ex)}), 400   # jsonify, if this is a json api