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https://issues.apache.org/jira/browse/AIRFLOW-3997?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ash Berlin-Taylor resolved AIRFLOW-3997.
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Resolution: Done
Fix Version/s: 1.10.3
> Add accessor for optional variables
> -----------------------------------
>
> Key: AIRFLOW-3997
> URL: https://issues.apache.org/jira/browse/AIRFLOW-3997
> Project: Apache Airflow
> Issue Type: Improvement
> Components: models
> Affects Versions: 1.10.2
> Reporter: Kristian Yrjölä
> Assignee: Kristian Yrjölä
> Priority: Minor
> Fix For: 1.10.3
>
>
> h4. TL;DR
> Proposing an addition to the _Variable_ accessors for optional variables. No
> change in existing functions.
>
> h4. Description
> Add a function to get a variable if it exists, and don't raise an error if it
> doesn't.
> *Rationale:*
> * The get function raises a _KeyError_ for a missing variable, if not careful
> that can bring down the whole application. Having a optional get function can
> make client code safer, isolating errors to the code using the specific
> variable only
> * Sometimes there is no obvious value to set as default, but you rather want
> to know if the variable is missing
> * The current get function doesn't support _None_ as a default value
> * Optional variables are good for feature flags for instance if you want to
> control certain behaviours between environments before it's released in
> production in a continuous deployment setup
> Passing in _default_var=None_ still raises a _KeyError_ since that is the
> default value of the _default_var_ parameter. If variable "foo" doesn't exist:
> {code:java}
> foo = Variable.get("foo", default_var=None)
> -> KeyError{code}
> You could use empty string or other values to indicate a missing variable,
> like this:
> {code:java}
> foo = Variable.get("foo", default_var="n/a")
> if foo == "n/a":
> handle_missing_foo(){code}
> *My proposal is this:*
> {code:java}
> foo = Variable.optional("foo")
> if foo is None:
> handle_missing_foo(){code}
> Which IMHO is more in line with Python's handling of a missing value.
> The function should still support the _serialize_json_ and _session_
> parameters, but not the _default_var_ parameter, since that would make little
> sense.
> Of course this can still be handled on the client side with a try-catch.
> However it can be a natural part of the API for the _Variable_ class,
> replacing many try-catches in client code.
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