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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 execute(cls, instance, async=True, countdown=2, is_heavy_task=False, **kwargs):
 """ Execute high level-operation """

        cls.pre_apply(instance, async=async, **kwargs)
        result = cls.apply_signature(instance, async=async, countdown=countdown,
                                     is_heavy_task=is_heavy_task, **kwargs)
        cls.post_apply(instance, async=async, **kwargs)
        return result