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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 get_callback_task(self, *args, **kwargs):
 """Returns a task for calling back this Pipeline. Args: params: Keyword argument containing a dictionary of key/value pairs that will be passed to the callback when it is executed. args, kwargs: Passed to the taskqueue.Task constructor. Use these arguments to set the task name (for idempotence), etc. Returns: A taskqueue.Task instance that must be enqueued by the caller. """

    if not self.async:
      raise UnexpectedPipelineError(
          'May only call get_callback_task() method for asynchronous pipelines.')

    params = kwargs.get('params', {})
    kwargs['params'] = params
    params['pipeline_id'] = self._pipeline_key.name()
    kwargs['url'] = self.base_path + '/callback'
    kwargs['method'] = 'POST'
    return taskqueue.Task(*args, **kwargs)