airflow sample to pass metadata to task. -----XCOM

1. At first, let us take a look at one sample which  one we do not need to pass the metadata

 

import random
from datetime import datetime, timedelta
from airflow.utils.dates import days_ago
from airflow.operators.python import PythonOperator
from airflow import DAG

default_args = {
    'owner': 'Jasmine Qian',
    'start_date': days_ago(0),
    'email': ['[email protected]'],
    'retries': 0,
    'retry_delay': timedelta(minutes=2),
}

dag = DAG(
    'Pass_Metadata',
    default_args=default_args,
    tags=['meta', 'params'],
    schedule_interval=None,
    catchup=False,
)


def run_this_fun(**context):
    print("Hi")


def check_state(**context):
    if random.random() > 0.7:
        raise Exception('Exception')
    print("I am OK")


run_this_task1 = PythonOperator(
    task_id="run_this",
    python_callable=check_state,
    provide_context=True,
    dag=dag,
)


run_this_task2 = PythonOperator(
    task_id="run_this2",
    python_callable=run_this_fun,
    provide_context=True,
    dag=dag,
)


run_this_task1 >> run_this_task2


# run_this_task2
if __name__ == "__main__":
    dag.cli()

 

 

2. how about task1 passing any metadata to task2?

import random
from datetime import datetime, timedelta
from airflow.utils.dates import days_ago
from airflow.operators.python import PythonOperator
from airflow import DAG

default_args = {
    'owner': 'Jasmine Qian',
    'start_date': days_ago(0),
    'email': ['[email protected]'],
    'retries': 0,
    'retry_delay': timedelta(minutes=2),
}

dag = DAG(
    'Pass_Metadata_v2',
    default_args=default_args,
    tags=['meta', 'params'],
    schedule_interval=None,
    catchup=False,
)


def run_this_fun(**context):
    received_value = context['ti'].xcom_pull(key='random_value')
    print("Hi, I received the value {}".format(str(received_value)))


def push_to_xcom(**context):
    random_value = random.random()
    context['ti'].xcom_push(key='random_value', value=random_value)
    print("I am OK")


run_this_task1 = PythonOperator(
    task_id="run_this",
    python_callable=push_to_xcom,
    provide_context=True,
    dag=dag,
)

run_this_task2 = PythonOperator(
    task_id="run_this2",
    python_callable=run_this_fun,
    provide_context=True,
    dag=dag,
)

run_this_task1 >> run_this_task2

# run_this_task2
if __name__ == "__main__":
    dag.cli()