Set custom property for encoding on werkzeug request

request.py

from werkzeug.wrappers import Request, Response
from werkzeug.formparser import FormDataParser
from werkzeug.serving import run_simple
from werkzeug.utils import cached_property
from werkzeug.datastructures import ImmutableMultiDict

def encode(value):
    #Catch encoding errors here
    return 'foo!'

class MixInRequest(Request):
    max_content_length = 1024 * 1024 * 4

    @cached_property
    def lcl_data(self):
        if self.method in ['POST','PUT','PATCH']:
            fields = dict([(key, encode(val)) for (key,val) in self.form.items()])
            return ImmutableMultiDict(fields)
        return None

class Shortly(object):

    def dispatch_request(self, request):
        print request.lcl_data
        return Response('Hello World!')

    def wsgi_app(self, environ, start_response):
        request = MixInRequest(environ)
        response = self.dispatch_request(request)
        return response(environ, start_response)

    def __call__(self, environ, start_response):
        return self.wsgi_app(environ, start_response)


def create_app():
    app = Shortly()
    return app


if __name__ == '__main__':
    app = create_app()
    run_simple('localhost', 8080, app, use_reloader=True)