[jira] [Created] (ZEPPELIN-1423) Allow users to specify pre/post-execute callbacks for interpreters

["Alex Goodman (JIRA)" <ji...@apache.org>]

Alex Goodman created ZEPPELIN-1423:
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             Summary: Allow users to specify pre/post-execute callbacks for interpreters
                 Key: ZEPPELIN-1423
                 URL: https://issues.apache.org/jira/browse/ZEPPELIN-1423
             Project: Zeppelin
          Issue Type: New Feature
          Components: Interpreters
    Affects Versions: 0.6.1
            Reporter: Alex Goodman
            Assignee: Alex Goodman
             Fix For: 0.7.0


Currently there is no easy way to specify 

With ZEPPELIN-1344, one of the requirements for interactive inline matplotlib plotting involves displaying images without explicitly calling a show() function. Eg,

{code}
import matplotlib.pyplot as plt
plt.plot([1, 2, 3])
{code}

should display an inline image even without calling {{plt.show()}} if mpl's interactive flag is enabled.

Currently this could be done in the pyspark interpreter by binding the figure's byte-string representation to the AngularDisplay system (since that can easily be updated through the matplotlib backend) but closing the figures (ie freeing up memory) would have to manually be done by the user. Thus we would need a post-execute callback that displays / cleans up all the active figure objects.

I will attempt to implement this using a new InterpreterCallback interface which includes support for two event types, pre and post-execute (relative to the paragraph). This would ideally lay down the foundation to make it possible for users to specify their callback code to the interpreter. 



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