With code, how do you update an airflow variable?

Question

I need to update a variable I have made in Airflow programmatically but I can not find the answer on how to do that with code.

I have retrieved my variable with this code:

column_number = Variable.get('column_number')

At the end of the function, I would like to increment the column_number by one

I have tried this: Variable.set_val("column_number", int(column_number) + 1)

And it does not work.

Here is the full code for reference:

import airflow from datetime import datetime, timedelta from random import randint from airflow import DAG from airflow.hooks.postgres_hook import PostgresHook from airflow.models import Variable from airflow.operators.python_operator import PythonOperator  args = {     'owner': 'besteman',     'start_date': datetime.utcnow(),     'retries': 1,     'retry_delay': timedelta(minutes=30) }  dag = DAG(dag_id='test-postgres', default_args=args, schedule_interval='@hourly')  def add_columns_and_values():      column_number = Variable.get('column_number')      pg_hook = PostgresHook(postgres_conn_id='airflow-test')      add_columns = f'ALTER TABLE students ADD COLUMN test{column_number} smallint;'      pg_hook.run(add_columns)       for i in range(8):         add_values = f"UPDATE students SET test{column_number} = '{randint(50, 100)}' WHERE id = {i+1};"         pg_hook.run(add_values)      Variable.set_val("column_number", int(column_number) + 1)   t1 = PythonOperator(task_id='add_columns_values',     python_callable=add_columns_and_values,     dag=dag) 

Answer 1

Use Variable.set instead of Variable.set_val. set_val() is a setter for the val attribute and not intended for outside use. This should do what you want:

Variable.set("column_number", int(column_number) + 1) 

It will make the actual update to the database, along with handling session and serialization for you if needed.

Reference: https://github.com/apache/incubator-airflow/blob/1.10.1/airflow/models.py#L4558-L4569