[GitHub] ashb opened a new pull request #3787: [AIRFLOW-2574] Cope with '%' in SQLA DSN when running migrations

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ashb opened a new pull request #3787: [AIRFLOW-2574] Cope with '%' in SQLA DSN when running migrations
URL: https://github.com/apache/incubator-airflow/pull/3787
 
 
   
   
   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.
     - https://issues.apache.org/jira/browse/AIRFLOW-2574
   
   ### Description
   
   Alembic uses a ConfigParser like Airflow does, and "%% is a special
   value in there, so we need to escape it. As per the Alembic docs:
   
   > Note that this value is passed to ConfigParser.set, which supports
   > variable interpolation using pyformat (e.g. `%(some_value)s`). A raw
   > percent sign not part of an interpolation symbol must therefore be
   > escaped, e.g. `%%`
   
   ### Tests
   
   - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason: Very hard to test this, as running unit tests _needs_ the DB to already exist.
   
   ### 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.
     - When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added.
   
   ### Code Quality
   
   - [x] Passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
   

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