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"""Example DAG demonstrating the usage of XComs."""
from airflow import DAG
from airflow.operators.python import PythonOperator
from airflow.utils.dates import days_ago

value_1 = [1, 2, 3]
value_2 = {'a': 'b'}


def push(**kwargs):
    """Pushes an XCom without a specific target"""
    kwargs['ti'].xcom_push(key='value from pusher 1', value=value_1)


def push_by_returning(**kwargs):
    """Pushes an XCom without a specific target, just by returning it"""
    return value_2


def puller(**kwargs):
    """Pull all previously pushed XComs and check if the pushed values match the pulled values."""
    ti = kwargs['ti']

    # get value_1
    pulled_value_1 = ti.xcom_pull(key=None, task_ids='push')
    if pulled_value_1 != value_1:
        raise ValueError(f'The two values differ {pulled_value_1} and {value_1}')

    # get value_2
    pulled_value_2 = ti.xcom_pull(task_ids='push_by_returning')
    if pulled_value_2 != value_2:
        raise ValueError(f'The two values differ {pulled_value_2} and {value_2}')

    # get both value_1 and value_2
    pulled_value_1, pulled_value_2 = ti.xcom_pull(key=None, task_ids=['push', 'push_by_returning'])
    if pulled_value_1 != value_1:
        raise ValueError(f'The two values differ {pulled_value_1} and {value_1}')
    if pulled_value_2 != value_2:
        raise ValueError(f'The two values differ {pulled_value_2} and {value_2}')


with DAG(
    'example_xcom',
    schedule_interval="@once",
    start_date=days_ago(2),
    default_args={'owner': 'airflow'},
    tags=['example'],
) as dag:

    push1 = PythonOperator(
        task_id='push',
        python_callable=push,
    )

    push2 = PythonOperator(
        task_id='push_by_returning',
        python_callable=push_by_returning,
    )

    pull = PythonOperator(
        task_id='puller',
        python_callable=puller,
    )

    pull << [push1, push2]
