airflow/example_dags/example_xcom.py

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"""Example DAG demonstrating the usage of XComs."""
from __future__ import annotations

import pendulum

from airflow import DAG, XComArg
from airflow.decorators import task
from airflow.operators.bash import BashOperator

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


@task
def push(ti=None):
    """Pushes an XCom without a specific target"""
    ti.xcom_push(key="value from pusher 1", value=value_1)


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


def _compare_values(pulled_value, check_value):
    if pulled_value != check_value:
        raise ValueError(f"The two values differ {pulled_value} and {check_value}")


@task
def puller(pulled_value_2, ti=None):
    """Pull all previously pushed XComs and check if the pushed values match the pulled values."""
    pulled_value_1 = ti.xcom_pull(task_ids="push", key="value from pusher 1")

    _compare_values(pulled_value_1, value_1)
    _compare_values(pulled_value_2, value_2)


@task
def pull_value_from_bash_push(ti=None):
    bash_pushed_via_return_value = ti.xcom_pull(key="return_value", task_ids="bash_push")
    bash_manually_pushed_value = ti.xcom_pull(key="manually_pushed_value", task_ids="bash_push")
    print(f"The xcom value pushed by task push via return value is {bash_pushed_via_return_value}")
    print(f"The xcom value pushed by task push manually is {bash_manually_pushed_value}")


with DAG(
    "example_xcom",
    schedule="@once",
    start_date=pendulum.datetime(2021, 1, 1, tz="UTC"),
    catchup=False,
    tags=["example"],
) as dag:
    bash_push = BashOperator(
        task_id="bash_push",
        bash_command='echo "bash_push demo"  && '
        'echo "Manually set xcom value '
        '{{ ti.xcom_push(key="manually_pushed_value", value="manually_pushed_value") }}" && '
        'echo "value_by_return"',
    )

    bash_pull = BashOperator(
        task_id="bash_pull",
        bash_command='echo "bash pull demo" && '
        f'echo "The xcom pushed manually is {XComArg(bash_push, key="manually_pushed_value")}" && '
        f'echo "The returned_value xcom is {XComArg(bash_push)}" && '
        'echo "finished"',
        do_xcom_push=False,
    )

    python_pull_from_bash = pull_value_from_bash_push()

    [bash_pull, python_pull_from_bash] << bash_push

    puller(push_by_returning()) << push()