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from werkzeug.wrappers import Request, Response

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from werkzeug.exceptions import (

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        HTTPException,

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        BadRequest,         # 400

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        NotFound,           # 404

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)

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from werkzeug.utils import redirect

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class Application:

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    URLS = None

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    def __init__ (self, urls=None):

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        """

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            urls        - werkzeug.routing.Map -> Handler

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        """

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        if not urls:

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            urls = self.URLS

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        if not urls:

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            raise ValueError("Required URLS/urls=...")

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        self.urls = urls

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    def respond (self, request):

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        """

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            Lookup Request -> Handler, params -> Response

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        """

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        # bind to request

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        urls = self.urls.bind_to_environ(request)

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        # lookup

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        handler, params = urls.match()

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        # handler instance

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        handler = handler(self, request, urls)

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        try :

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            handler.init()

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            # apply

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            return handler.respond(**params)

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        finally :

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            handler.cleanup()

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    @Request.application

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    def __call__ (self, request) :

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        """

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            WSGI entry point, werkzeug Request -> Response

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        """

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        try :

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            return self.respond(request)

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        except HTTPException as ex :

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            return ex

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class Handler (object) :

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    """

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        Per-Request controller/view, containing the request context and generating the response.

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    """

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    # werkzeug defaults to UTF-8

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    MIMETYPE = 'text/html'

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    def __init__ (self, app, request, urls) :

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        """

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            app     - wsgi.Application

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            request - werkzeug.Request

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            urls    - werkzeug.routing.Map.bind_to_environ()

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        """

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        self.app = app

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        self.request = request

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        self.urls = urls

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    def url (self, handler=None, **params) :

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        """

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            Return an URL for given endpoint, with parameters,

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        """

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        if not handler :

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            handler = self.__class__

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        return self.urls.build(handler, params)

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    ## processing stages

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    def init (self) :

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        """

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            Initialize on request start.

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        """

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        pass

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    def process (self, **params) :

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        """

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            Process request args to build internal request state.

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            May optionally return a Response, to e.g. redirect after POST.

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        """

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        pass

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    def render (self) :

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        """

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            Render response.

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        """

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        raise NotImplementedError()

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    def mimetype (self):

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        return self.MIMETYPE

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    def status (self):

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        return 200

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    def respond (self, **params) :

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        """

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            Generate a response, or raise an HTTPException

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        """

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        # returning e.g. redirect?

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        response = self.process(**params)

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        if response :

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            return response

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        return Response(self.render_response(), mimetype=self.mimetype(), status=self.status())

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    def cleanup (self) :

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        """

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            After request processing. Do not fail :)

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        """

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        pass

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