Framework Support

Decorator Usage

When using the :meth:`use_args <webargs.flaskparser.FlaskParser.use_args>` decorator, the arguments dictionary will be before any URL variable parameters.

from webargs import fields
from webargs.flaskparser import use_args


@app.route("/user/<int:uid>")
@use_args({"per_page": fields.Int()}, location="query")
def user_detail(args, uid):
    return ("The user page for user {uid}, showing {per_page} posts.").format(
        uid=uid, per_page=args["per_page"]
    )

Error Handling

Webargs uses Flask's abort function to raise an HTTPException when a validation error occurs. If you use the Flask.errorhandler method to handle errors, you can access validation messages from the messages attribute of the attached ValidationError.

Here is an example error handler that returns validation messages to the client as JSON.

from flask import jsonify


# Return validation errors as JSON
@app.errorhandler(422)
@app.errorhandler(400)
def handle_error(err):
    headers = err.data.get("headers", None)
    messages = err.data.get("messages", ["Invalid request."])
    if headers:
        return jsonify({"errors": messages}), err.code, headers
    else:
        return jsonify({"errors": messages}), err.code

URL Matches

The FlaskParser supports parsing values from a request's view_args.

from webargs.flaskparser import use_args


@app.route("/greeting/<name>/")
@use_args({"name": fields.Str()}, location="view_args")
def greeting(args, **kwargs):
    return "Hello {}".format(args["name"])

Decorator Usage

When using the :meth:`use_args <webargs.djangoparser.DjangoParser.use_args>` decorator, the arguments dictionary will positioned after the request argument.

Function-based Views

from django.http import HttpResponse
from webargs import Arg
from webargs.djangoparser import use_args

account_args = {
    "username": fields.Str(required=True),
    "password": fields.Str(required=True),
}


@use_args(account_args, location="form")
def login_user(request, args):
    if request.method == "POST":
        login(args["username"], args["password"])
    return HttpResponse("Login page")

Class-based Views

from django.views.generic import View
from django.shortcuts import render_to_response
from webargs import fields
from webargs.djangoparser import use_args

blog_args = {"title": fields.Str(), "author": fields.Str()}


class BlogPostView(View):
    @use_args(blog_args, location="query")
    def get(self, request, args):
        blog_post = Post.objects.get(title__iexact=args["title"], author=args["author"])
        return render_to_response("post_template.html", {"post": blog_post})

Error Handling

The :class:`DjangoParser` does not override :meth:`handle_error <webargs.core.Parser.handle_error>`, so your Django views are responsible for catching any :exc:`ValidationErrors` raised by the parser and returning the appropriate HTTPResponse.

from django.http import JsonResponse

from webargs import fields, ValidationError, json

argmap = {"name": fields.Str(required=True)}


def index(request):
    try:
        args = parser.parse(argmap, request)
    except ValidationError as err:
        return JsonResponse(err.messages, status=422)
    except json.JSONDecodeError:
        return JsonResponse({"json": ["Invalid JSON body."]}, status=400)
    return JsonResponse({"message": "Hello {name}".format(name=name)})

Decorator Usage

When using the :meth:`use_args <webargs.tornadoparser.TornadoParser.use_args>` decorator, the decorated method will have the dictionary of parsed arguments passed as a positional argument after self and any regex match groups from the URL spec.

from webargs import fields
from webargs.tornadoparser import use_args


class HelloHandler(tornado.web.RequestHandler):
    @use_args({"name": fields.Str()})
    def post(self, id, reqargs):
        response = {"message": "Hello {}".format(reqargs["name"])}
        self.write(response)


application = tornado.web.Application([(r"/hello/([0-9]+)", HelloHandler)], debug=True)

As with the other parser modules, :meth:`use_kwargs <webargs.tornadoparser.TornadoParser.use_kwargs>` will add keyword arguments to the view callable.

Error Handling

A HTTPError <webargs.tornadoparser.HTTPError> will be raised in the event of a validation error. Your RequestHandlers are responsible for handling these errors.

Here is how you could write the error messages to a JSON response.

from tornado.web import RequestHandler


class MyRequestHandler(RequestHandler):
    def write_error(self, status_code, **kwargs):
        """Write errors as JSON."""
        self.set_header("Content-Type", "application/json")
        if "exc_info" in kwargs:
            etype, exc, traceback = kwargs["exc_info"]
            if hasattr(exc, "messages"):
                self.write({"errors": exc.messages})
                if getattr(exc, "headers", None):
                    for name, val in exc.headers.items():
                        self.set_header(name, val)
                self.finish()

Decorator Usage

When using the :meth:`use_args <webargs.pyramidparser.PyramidParser.use_args>` decorator on a view callable, the arguments dictionary will be positioned after the request argument.

from pyramid.response import Response
from webargs import fields
from webargs.pyramidparser import use_args


@use_args({"uid": fields.Str(), "per_page": fields.Int()}, location="query")
def user_detail(request, args):
    uid = args["uid"]
    return Response(
        "The user page for user {uid}, showing {per_page} posts.".format(
            uid=uid, per_page=args["per_page"]
        )
    )

As with the other parser modules, :meth:`use_kwargs <webargs.pyramidparser.PyramidParser.use_kwargs>` will add keyword arguments to the view callable.

URL Matches

The PyramidParser supports parsing values from a request's matchdict.

from pyramid.response import Response
from webargs.pyramidparser import use_args


@use_args({"mymatch": fields.Int()}, location="matchdict")
def matched(request, args):
    return Response("The value for mymatch is {}".format(args["mymatch"]))

Decorator Usage

When using the :meth:`use_args <webargs.falconparser.FalconParser.use_args>` decorator on a resource method, the arguments dictionary will be positioned directly after the request and response arguments.

import falcon
from webargs import fields
from webargs.falconparser import use_args


class BlogResource:
    request_args = {"title": fields.Str(required=True)}

    @use_args(request_args)
    def on_post(self, req, resp, args, post_id):
        content = args["title"]
        # ...


api = application = falcon.API()
api.add_route("/blogs/{post_id}")

As with the other parser modules, :meth:`use_kwargs <webargs.falconparser.FalconParser.use_kwargs>` will add keyword arguments to your resource methods.

Hook Usage

You can easily implement hooks by using parser.parse <webargs.falconparser.FalconParser.parse> directly.

import falcon
from webargs import fields
from webargs.falconparser import parser


def add_args(argmap, **kwargs):
    def hook(req, resp, resource, params):
        parsed_args = parser.parse(argmap, req=req, **kwargs)
        req.context["args"] = parsed_args

    return hook


@falcon.before(add_args({"page": fields.Int()}, location="query"))
class AuthorResource:
    def on_get(self, req, resp):
        args = req.context["args"]
        page = args.get("page")
        # ...

Decorator Usage

When using the :meth:`use_args <webargs.aiohttpparser.AIOHTTPParser.use_args>` decorator on a handler, the parsed arguments dictionary will be the last positional argument.

import asyncio

from aiohttp import web
from webargs import fields
from webargs.aiohttpparser import use_args


@use_args({"content": fields.Str(required=True)})
async def create_comment(request, args):
    content = args["content"]
    # ...


app = web.Application()
app.router.add_route("POST", "/comments/", create_comment)

As with the other parser modules, :meth:`use_kwargs <webargs.aiohttpparser.AIOHTTPParser.use_kwargs>` will add keyword arguments to your resource methods.

Usage with coroutines

The :meth:`use_args <webargs.aiohttpparser.AIOHTTPParser.use_args>` and :meth:`use_kwargs <webargs.aiohttpparser.AIOHTTPParser.use_kwargs>` decorators will work with both async def coroutines and generator-based coroutines decorated with asyncio.coroutine.

import asyncio

from aiohttp import web
from webargs import fields
from webargs.aiohttpparser import use_kwargs

hello_args = {"name": fields.Str(missing="World")}

# The following are equivalent


@asyncio.coroutine
@use_kwargs(hello_args)
def hello(request, name):
    return web.Response(body="Hello, {}".format(name).encode("utf-8"))


@use_kwargs(hello_args)
async def hello(request, name):
    return web.Response(body="Hello, {}".format(name).encode("utf-8"))

URL Matches

The AIOHTTPParser <webargs.aiohttpparser.AIOHTTPParser> supports parsing values from a request's match_info.

from aiohttp import web
from webargs.aiohttpparser import use_args


@parser.use_args({"slug": fields.Str()}, location="match_info")
def article_detail(request, args):
    return web.Response(body="Slug: {}".format(args["slug"]).encode("utf-8"))


app = web.Application()
app.router.add_route("GET", "/articles/{slug}", article_detail)

Decorator Usage

The preferred way to apply decorators to Bottle routes is using the apply argument.

from bottle import route

user_args = {"name": fields.Str(missing="Friend")}


@route("/users/<_id:int>", method="GET", apply=use_args(user_args))
def users(args, _id):
    """A welcome page."""
    return {"message": "Welcome, {}!".format(args["name"]), "_id": _id}