def allocate_dynamic_segment(self, context, network_id, segment):
        """Allocate a dynamic segment using a partial or full segment dict."""
        dynamic_segment = segments_db.get_dynamic_segment(
            context, network_id, segment.get(api.PHYSICAL_NETWORK),
            segment.get(api.SEGMENTATION_ID))

        if dynamic_segment:
            return dynamic_segment

        driver = self.drivers.get(segment.get(api.NETWORK_TYPE))
        if isinstance(driver.obj, api.TypeDriver):
            dynamic_segment = driver.obj.reserve_provider_segment(
                context.session, segment)
        else:
            dynamic_segment = driver.obj.reserve_provider_segment(
                context, segment)
        segments_db.add_network_segment(context, network_id, dynamic_segment,
                                        is_dynamic=True)
        return dynamic_segment