airflow/example_dags/example_nested_branch_dag.py

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"""
Example DAG demonstrating a workflow with nested branching. The join tasks are created with
``none_failed_or_skipped`` trigger rule such that they are skipped whenever their corresponding
``BranchPythonOperator`` are skipped.
"""

from airflow.models import DAG
from airflow.operators.dummy import DummyOperator
from airflow.operators.python import BranchPythonOperator
from airflow.utils.dates import days_ago

with DAG(
    dag_id="example_nested_branch_dag", start_date=days_ago(2), schedule_interval="@daily", tags=["example"]
) as dag:
    branch_1 = BranchPythonOperator(task_id="branch_1", python_callable=lambda: "true_1")
    join_1 = DummyOperator(task_id="join_1", trigger_rule="none_failed_or_skipped")
    true_1 = DummyOperator(task_id="true_1")
    false_1 = DummyOperator(task_id="false_1")
    branch_2 = BranchPythonOperator(task_id="branch_2", python_callable=lambda: "true_2")
    join_2 = DummyOperator(task_id="join_2", trigger_rule="none_failed_or_skipped")
    true_2 = DummyOperator(task_id="true_2")
    false_2 = DummyOperator(task_id="false_2")
    false_3 = DummyOperator(task_id="false_3")

    branch_1 >> true_1 >> join_1
    branch_1 >> false_1 >> branch_2 >> [true_2, false_2] >> join_2 >> false_3 >> join_1