title: Assign airflow task to several DAGs
body: <p>I am trying to reuse an existing airflow task by assigning it to different dags.</p>
  <pre><code>def create_new_task_for_dag(task: BaseOperator,
                          dag: models.DAG) -&gt; BaseOperator:
      &quot;&quot;&quot;Create a deep copy of given task and associate it with given dag
      &quot;&quot;&quot;
      new_task = copy.deepcopy(task)
      new_task.dag = dag
      return new_task
  
  
  print_datetime_task = python_operator.PythonOperator(
      task_id='print_datetime', python_callable=_print_datetime)
  
  # define a new dag ...
  # add to the new dag
  create_new_task_for_dag(print_datetime_task, new_dag)
  </code></pre>
  <p>Then it gives the error <code>Task is missing the start_date parameter</code>.
  If I define the dag when creating the operator, <code>print_datetime_task = PythonOperator(task_id='print_datetime', python_callable=_print_datetime, dag=new_dag)</code>, then it is OK.</p>
  <p>I have searched around, and this seems to be the root cause: <a href="https://github.com/apache/airflow/pull/5598" rel="nofollow noreferrer">https://github.com/apache/airflow/pull/5598</a>, but PR has been marked as stale.</p>
  <p>I wonder if there is any other approach to reuse an existing airflow task assign to a different dag.</p>
  <p>I am using <code>apache-airflow[docker,kubernetes]==1.10.10</code></p>