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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 main_callback(self, *args, **kwargs):
 """ Main callback called when an event is received from an entry point. :returns: The entry point's callback. :rtype: function :raises NotImplementedError: When the entrypoint doesn't have the required attributes. """

        if not self.callback:
            raise NotImplementedError('Entrypoints must declare `callback`')
        if not self.settings:
            raise NotImplementedError('Entrypoints must declare `settings`')

        self.callback.im_self.db = None

        #1. Start all the middlewares
        with self.debug(*args, **kwargs):
            with self.database():
                #2. `Real` callback
                result = self.callback(*args, **kwargs)#pylint: disable=not-callable
        return result