[GitHub] [airflow] michaelmdeng opened a new pull request #5755: [AIRFLOW-4568] Add unallowed_states to ExternalTaskSensor

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michaelmdeng opened a new pull request #5755: [AIRFLOW-4568] Add unallowed_states to ExternalTaskSensor
URL: https://github.com/apache/airflow/pull/5755
 
 
   
   
   
   Make sure you have checked _all_ steps below.
   
   ### Jira
   
   - [x] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "\[AIRFLOW-XXX\] My Airflow PR"
     - https://issues.apache.org/jira/browse/AIRFLOW-4568
     - In case you are fixing a typo in the documentation you can prepend your commit with \[AIRFLOW-XXX\], code changes always need a Jira issue.
     - In case you are proposing a fundamental code change, you need to create an Airflow Improvement Proposal ([AIP](https://cwiki.apache.org/confluence/display/AIRFLOW/Airflow+Improvements+Proposals)).
     - In case you are adding a dependency, check if the license complies with the [ASF 3rd Party License Policy](https://www.apache.org/legal/resolved.html#category-x).
   
   Also possibly dupe of [AIRFLOW-104]??
   
   ### Description
   
   - [x] Here are some details about my PR, including screenshots of any UI changes:
   
   Often times we want an ExternalTaskSensor to not behave as a sensor (poke until a condition is satisfied), and instead as a mirror of a task in another dag (succeed if the external succeeds, fail if the external fails).
   
   This change adds the `unallowed_states` parameter to the ExternalTaskSensor. If external task/dag is found to be in `unallowed_states`, the sensor will immediately fail instead of previous behavior of returning false and continuing to poke until timeout.
   
   ### Tests
   
   - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
   Additional tests in tests/sensors/test_external_task_sensor.py
   
   ### Commits
   
   - [x] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Documentation
   
   - [x] In case of new functionality, my PR adds documentation that describes how to use it.
     - All the public functions and the classes in the PR contain docstrings that explain what it does
     - If you implement backwards incompatible changes, please leave a note in the [Updating.md](https://github.com/apache/airflow/blob/master/UPDATING.md) so we can assign it to a appropriate release
   
   ### Code Quality
   
   - [x] Passes `flake8`
   

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