More templates

Introduction to Apache Airflow in Python

Mike Metzger

Data Engineer

Quick task reminder

Take a list of filenames
Print "Reading <filename>" to the log / output

Templated version:

templated_command="""
echo "Reading {{ params.filename }}"
"""
t1 = BashOperator(task_id='template_task',
     bash_command=templated_command,
     params={'filename': 'file1.txt'},
     dag=example_dag)

More advanced template

templated_command="""
{% for filename in params.filenames %}

  echo "Reading {{ filename }}"

{% endfor %}
"""

t1 = BashOperator(task_id='template_task',
       bash_command=templated_command,
       params={'filenames': ['file1.txt', 'file2.txt']},
       dag=example_dag)

Reading file1.txt
Reading file2.txt

Variables

Airflow built-in runtime variables
Provides assorted information about DAG runs, tasks, and even the system configuration.
Examples include:

Execution Date: {{ ds }}                              # YYYY-MM-DD
Execution Date, no dashes: {{ ds_nodash }}            # YYYYMMDD

Previous Execution date: {{ prev_ds }}                # YYYY-MM-DD
Prev Execution date, no dashes: {{ prev_ds_nodash }}  # YYYYMMDD

DAG object: {{ dag }}

Airflow config object: {{ conf }}

¹ https://airflow.apache.org/docs/stable/macros-ref.html

Macros

In addition to others, there is also a {{ macros }} variable.

This is a reference to the Airflow macros package which provides various useful objects / methods for Airflow templates.

{{ macros.datetime }}: The datetime.datetime object
{{ macros.timedelta }}: The timedelta object
{{ macros.uuid }}: Python's uuid object
{{ macros.ds_add('2020-04-15', 5) }}: Modify days from a date, this example returns 2020-04-20

Let's practice!

Introduction to Apache Airflow in Python