ashb commented on code in PR #74274: URL: https://github.com/apache/airflow/pull/74274#discussion_r4197432374
########## airflow-core/docs/authoring-and-scheduling/loops.rst: ########## @@ -0,0 +1,339 @@ + .. Licensed to the Apache Software Foundation (ASF) under one + or more contributor license agreements. See the NOTICE file + distributed with this work for additional information + regarding copyright ownership. The ASF licenses this file + to you 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 + + .. http://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. + +.. _loops: + +Loops +===== + +A loop repeats a group of tasks a number of times decided at runtime, +using the results of each iteration. Each iteration can use the previous +iteration's result. Use a loop for work such as refining an answer, following +a hierarchy, or processing successive batches. + +A conditional loop works like a ``do … while`` loop: run the body, then test +whether to run it again. Airflow's ``until`` condition expresses when to stop, +so it corresponds to ``do { body } while not until(result)``. The body runs at +least once. ``max_iterations`` sets an upper bound; the runtime condition +determines how many iterations are needed within that bound. + +Tasks within an iteration can run in parallel. + +If you are not sure whether you need a loop or mapped tasks, see +:ref:`loops-and-mapped-tasks`. + +Create a loop +------------- + +Define the body with ``@task_group`` and call ``.loop()`` on the decorated +function. Supply a positive integer ``max_iterations`` to bound the number of +iterations. An optional ``until`` callable decides when to stop early. + +Airflow evaluates ``until`` in a gate task downstream of the body's terminal task: + +* ``True`` means stop: the condition has been met. +* ``False`` means continue, provided another iteration is allowed. + +Airflow creates the next iteration when the gate says to continue. +It does not create all ``max_iterations`` up front: +if the loop stops after four iterations, you see those four, without a tail +of skipped iterations. For a fixed-count loop, the gate continues until the +count is reached. Review Comment: Actually I'm not sure why I even mention gate for a fixed-count loop. The Gate may as not exist. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
