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# Copyright 2018 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""An example DAG demonstrating simple Apache Airflow operators."""
# [START composer_simple]
# [START composer_simple_define_dag]
import datetime
from airflow import models
# [END composer_simple_define_dag]
# [START composer_simple_operators]
from airflow.operators.bash import BashOperator
from airflow.operators.python import PythonOperator
# [END composer_simple_operators]
# [START composer_simple_define_dag]
default_dag_args = {
# The start_date describes when a DAG is valid / can be run. Set this to a
# fixed point in time rather than dynamically, since it is evaluated every
# time a DAG is parsed. See:
# https://airflow.apache.org/faq.html#what-s-the-deal-with-start-date
"start_date": datetime.datetime(2018, 1, 1),
}
# Define a DAG (directed acyclic graph) of tasks.
# Any task you create within the context manager is automatically added to the
# DAG object.
with models.DAG(
"composer_sample_simple_greeting",
schedule_interval=datetime.timedelta(days=1),
default_args=default_dag_args,
) as dag:
# [END composer_simple_define_dag]
# [START composer_simple_operators]
def greeting():
import logging
logging.info("Hello World!")
# An instance of an operator is called a task. In this case, the
# hello_python task calls the "greeting" Python function.
hello_python = PythonOperator(task_id="hello", python_callable=greeting)
# Likewise, the goodbye_bash task calls a Bash script.
goodbye_bash = BashOperator(task_id="bye", bash_command="echo Goodbye.")
# [END composer_simple_operators]
# [START composer_simple_relationships]
# Define the order in which the tasks complete by using the >> and <<
# operators. In this example, hello_python executes before goodbye_bash.
hello_python >> goodbye_bash
# [END composer_simple_relationships]
# [END composer_simple]