Code / API
==========

Operators
---------
Operators allow for generation of certain types of tasks that become nodes in
the DAG when instantiated. All operators derive from BaseOperator and
inherit many attributes and methods that way. Refer to the BaseOperator
documentation for more details.

There are 3 main types of operators:

- Operators that performs an **action**, or tell another system to
  perform an action
- **Transfer** operators move data from one system to another
- **Sensors** are a certain type of operator that will keep running until a
  certain criterion is met. Examples include a specific file landing in HDFS or
  S3, a partition appearing in Hive, or a specific time of the day. Sensors
  are derived from ``BaseSensorOperator`` and run a poke
  method at a specified ``poke_interval`` until it returns ``True``.

.. automodule:: airflow.operators
    :show-inheritance:
    :members:
        BashOperator,
        BranchPythonOperator,
        DummyOperator,
        EmailOperator,
        ExternalTaskSensor,
        HdfsSensor,
        Hive2SambaOperator,
        HiveOperator,
        HivePartitionSensor,
        HiveToMySqlTransfer,
        SimpleHttpOperator,
        HttpSensor,
        MySqlOperator,
        MySqlToHiveTransfer,
        PostgresOperator,
        PrestoCheckOperator,
        PrestoIntervalCheckOperator,
        PrestoValueCheckOperator,
        PythonOperator,
        S3KeySensor,
        S3ToHiveTransfer,
        SqlSensor,
        SubDagOperator,
        TimeSensor

Macros
---------
Here's a list of variables and macros that can be used in templates


Default Variables
'''''''''''''''''
The Airflow engine passes a few variables by default that are accessible
in all templates

=================================   ====================================
Variable                            Description
=================================   ====================================
``{{ ds }}``                        the execution date as ``YYYY-MM-DD``
``{{ yesterday_ds }}``              yesterday's date as  ``YYYY-MM-DD``
``{{ tomorrow_ds }}``               tomorrow's date as  ``YYYY-MM-DD``
``{{ ds }}``                        the execution date as ``YYYY-MM-DD``
``{{ execution_date }}``            the execution_date, (datateime.datetime)
``{{ dag }}``                       the DAG object
``{{ task }}``                      the Task object
``{{ macros }}``                    a reference to the macros package, described bellow
``{{ task_instance }}``             the task_instance object
``{{ ds_nodash }}``                 the execution date as ``YYYYMMDD``
``{{ end_date }}``                  same as ``{{ ds }}``
``{{ lastest_date }}``              same as ``{{ ds }}``
``{{ ti }}``                        same as ``{{ task_instance }}``
``{{ params }}``                    a reference to the user defined params dictionary
``{{ task_instance_key_str }}``     a unique, human readable key to the task instance
                                    formatted ``{dag_id}_{task_id}_{ds}``
=================================   ====================================

Note that you can access the object's attributes and methods with simple
dot notation. Here are some examples of what is possible:
``{{ task.owner }}``, ``{{ task.task_id }}``, ``{{ ti.hostname }}``, ...
Refer to the models documentation for more information on the objects'
attributes and methods.

Macros
''''''
These macros live under the ``macros`` namespace in your templates.

.. automodule:: airflow.macros
    :show-inheritance:
    :members:

.. automodule:: airflow.macros.hive
    :show-inheritance:
    :members:

.. _models_ref:

Models
------

Models are built on top of th SQLAlchemy ORM Base class, and instances are
persisted in the database.


.. automodule:: airflow.models
    :show-inheritance:
    :members: DAG, BaseOperator, TaskInstance, DagBag, Connection

Hooks
-----
.. automodule:: airflow.hooks
    :show-inheritance:
    :members: MySqlHook, PostgresHook, PrestoHook, HiveCliHook, HiveServer2Hook, HiveMetastoreHook, HttpHook, S3Hook, SqliteHook

Executors
---------
Executors are the mechanism by which task instances get run.

.. automodule:: airflow.executors
    :show-inheritance:
    :members: LocalExecutor, CeleryExecutor, SequentialExecutor