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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def serializer(self, req):
 """ Selects and returns the serializer to use, based on the serializers declared on the action method and its extensions. The returned content type is selected based on the types available and the best match generated from the HTTP `Accept` header. Raises `HTTPNotAcceptable` if the request cannot be serialized to an acceptable media type. Returns a tuple of the content type and the serializer. """


        # Select the best match serializer
        content_types = self.method.serializers.get_types()
        content_type = req.accept.best_match(content_types)
        if content_type is None:
            raise webob.exc.HTTPNotAcceptable()

        # Select the serializer to use
        try:
            serializer = self.method.serializers(content_type)
        except KeyError:
            raise webob.exc.HTTPNotAcceptable()

        # If it has an attacher, attach all the serializers for the
        # extensions
        if hasattr(serializer, 'attach'):
            for ext in reversed(self.extensions):
                try:
                    serializer.attach(ext.serializers(content_type))
                except KeyError:
                    pass

        # Return content type and serializer
        return content_type, serializer