Get all Airflow Leaf Nodes/Tasks

Question

I want to build something where I need to capture all of the leaf tasks and add a downstream dependency to them to make a job complete in our database. Is there an easy way to find all the leaf nodes of a DAG in Airflow?

Answer 1

Use upstream_task_ids and downstream_task_ids @property from BaseOperator

def get_start_tasks(dag: DAG) -> List[BaseOperator]:
    # returns list of "head" / "root" tasks of DAG
    return [task for task in dag.tasks if not task.upstream_task_ids]


def get_end_tasks(dag: DAG) -> List[BaseOperator]:
    # returns list of "leaf" tasks of DAG
    return [task for task in dag.tasks if not task.downstream_task_ids]

Type-Annotations from Python 3.6+

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UPDATE-1

Now Airflow DAG model has powerful @property functions like

• leaves
• roots
• topological_sort