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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 _cleanup_workflow(config, task_id, args, **kwargs):
 """ Cleanup the results of a workflow when it finished. Connects to the postrun signal of Celery. If the signal was sent by a workflow, remove the result from the result backend. Args: task_id (str):
 The id of the task. args (tuple):
 The arguments the task was started with. **kwargs: Keyword arguments from the hook. """

    from lightflow.models import Workflow
    if isinstance(args[0], Workflow):
        if config.celery['result_expires'] == 0:
            AsyncResult(task_id).forget()