Parsing arguments always returns None

parsing the arguments always returns None, even if trying the most basic syntax taken from the quick start page. Maybe I have a typo I failed to see.

Versions: Flask: 1.1.2 Marshmallow: 3.6.0 Flask-marshmallow: 0.12 webargs: 6.1.0

Code:

from pprint import pprint

from flask import request
from flask_restful import Resource
from webargs import fields, validate
from webargs.flaskparser import parser

# Flask-restful resource, GET method called with ?type=99999
class WebsiteList(Resource):
    @classmethod
    # @use_kwargs(website_args)
    def get(cls):
        website_args = {
            'type': fields.String(
                required=True,
                validate=validate.Range(min=0, max=6, error="testing error, never triggered")
            ),
        }

        # Line below outputs: ImmutableMultiDict([('type', '6')])
        pprint(request.args)

        args = parser.parse(website_args, request)
        # Line below outputs: None
        pprint(args)

I have also tried the decorator @use_kwargs(website_args) (And define website_args beforehand of course), but I get a traceback for TypeError: ‘NoneType’ object is not iterable:

Traceback (most recent call last):
  File "C:\Users\Marco\.virtualenvs\api-kHflOUBu\lib\site-packages\flask\app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "C:\Users\Marco\.virtualenvs\api-kHflOUBu\lib\site-packages\flask\app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "C:\Users\Marco\.virtualenvs\api-kHflOUBu\lib\site-packages\flask_restful\__init__.py", line 468, in wrapper
    resp = resource(*args, **kwargs)
  File "C:\Users\Marco\.virtualenvs\api-kHflOUBu\lib\site-packages\flask\views.py", line 89, in view
    return self.dispatch_request(*args, **kwargs)
  File "C:\Users\Marco\.virtualenvs\api-kHflOUBu\lib\site-packages\flask_restful\__init__.py", line 583, in dispatch_request
    resp = meth(*args, **kwargs)
  File "C:\Users\Marco\.virtualenvs\api-kHflOUBu\lib\site-packages\webargs\core.py", line 364, in wrapper
    args, kwargs, parsed_args, as_kwargs
  File "C:\Users\Marco\.virtualenvs\api-kHflOUBu\lib\site-packages\webargs\core.py", line 298, in _update_args_kwargs
    kwargs.update(parsed_args)
TypeError: 'NoneType' object is not iterable

[sirosen]

I just confirmed that this is not an incompatibility between webargs and flask-restful.

the following example, nearly identical to the OP's, produces a 422 error

from flask import request, Flask
from flask_restful import Resource, Api
from webargs import fields
from webargs.flaskparser import parser

app = Flask(__name__)
api = Api(app)


class Test(Resource):
    @classmethod
    def get(cls):
        argdef = {"type": fields.String(required=True)}
        print(request.args)
        args = parser.parse(argdef, request)
        print(args)


api.add_resource(Test, "/")


with app.test_client() as client:
    res = client.get("/")
    print("post_req: status=" + str(res.status_code))
    print("post_req: data:\n" + res.data.decode("utf-8"))

I think my prior guess that the validation error handler isn’t raising an exception is the best explanation. I’m going to open a PR which adds a warning log statement in that case, but I don’t think there’s anything further we can do here.

[sirosen]

I just took a crack at reproducing this issue without flask-restful and I looked at flask-restful source to see if there was anything obvious they’re doing which might trip us up.

this example, very similar to the provided one, works and fails with a 422

from flask import Flask

from webargs.flaskparser import parser
import marshmallow as ma

website_args = {"type": ma.fields.String(required=True)}

app = Flask(__name__)


@app.route("/func_1")
def func_1():
    print("func_1: start")
    res = parser.parse(website_args)
    print("func_1: parse done")
    print("func_1: res:" + str(res))
    print("func_1: stop")


with app.test_client() as client:
    res = client.get("/func_1")
    print("post_req: status=" + str(res.status_code))
    print("post_req: data:\n" + res.data.decode("utf-8"))

I’ve tried a few variations on this theme with just flask and webargs.

It’s possible that flask-restful is doing something wrong or just unexpected, but my suspicion is that in the OP’s case, flask.abort or parser._on_validation_error aren’t causing exceptions to be raised. Possibly flask-restful changes the behavior of abort? I’m not familiar enough with the framework to say.

I went back over our empty and null body handling for JSON data, and everything seems to lead back to the JSON data being missing, and we later convert that to {} to pass to the schema. But one thing I noticed is that the fallthrough condition for parse could produce None, if the user has defined an error handler which doesn’t raise an exception. I think this is what’s going on.