get_context_variable

    def get_context_variable(self, name):
        """
        Returns a variable from the context passed to the
        template. Only works if your version of Flask
        has signals support (0.6+) and blinker is installed.

        Raises a ContextVariableDoesNotExist exception if does
        not exist in context.

        :param name: name of variable
        """
        if not _is_signals:
            raise RuntimeError("Signals not supported")

        for template, context in self.templates:
            if name in context:
                return context[name]
        raise ContextVariableDoesNotExist