How to validate URL parameters in Flask app?

Question

I'm writing a RESTful API in Flask. I can access URL parameters via the Request Object. What is the best way to validate the given URL parameters?

For example:

/places?zip=97239 # This is a valid filter
/places?foo=bar   # This is not a valid filter, 404 response?

One solution is to search through request.args and compare each entry against a set of valid URL parameters. Is there a better way?

Thanks!

Answer 1

You can use the flask-parameter-validation library in order to validate within Flask. This is useful as it uses Flask features under-the-hood, handles files/forms, and implicitly converts Query parameters.

For your example, you would do the following:

from flask import Flask
from typing import Optional
from flask_parameter_validation import ValidateParameters, Query

app = Flask(__name__)


@app.route("/places", methods=["GET"])
@ValidateParameters()
def check_places(
        zip: Optional[int] = Query()
     ):
    return "Hello World!"


if __name__ == "__main__":
    app.run()

Answer 2

Put the GET parameters in a dictionary and validate it using voluptuous.

For example:

parameters = Schema({
    Required('zip'): Coerce(int),
})

will accept any dictionary with a "zip" key that has a value that can be coerced to an integer (so either 1 or "1" depending on how you get the values). You can then validate it using:

parameters(my_get_params)  # should not raise an exception