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82 lines
3.2 KiB
Markdown
82 lines
3.2 KiB
Markdown
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---
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layout: page
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title: "Interpreter Execution Hooks (Experimental)"
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description: "Apache Zeppelin allows for users to specify additional code to be executed by an interpreter at pre and post-paragraph code execution."
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group: manual
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---
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<!--
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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{% include JB/setup %}
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# Interpreter Execution Hooks (Experimental)
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<div id="toc"></div>
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## Overview
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Apache Zeppelin allows for users to specify additional code to be executed by an interpreter at pre and post-paragraph code execution.
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This is primarily useful if you need to run the same set of code for all of the paragraphs within your notebook at specific times.
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Currently, this feature is only available for the spark and pyspark interpreters.
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To specify your hook code, you may use `z.registerHook()`.
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For example, enter the following into one paragraph:
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```python
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%pyspark
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z.registerHook("post_exec", "print 'This code should be executed before the parapgraph code!'")
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z.registerHook("pre_exec", "print 'This code should be executed after the paragraph code!'")
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```
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These calls will not take into effect until the next time you run a paragraph.
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In another paragraph, enter
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```python
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%pyspark
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print "This code should be entered into the paragraph by the user!"
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```
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The output should be:
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```
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This code should be executed before the paragraph code!
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This code should be entered into the paragraph by the user!
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This code should be executed after the paragraph code!
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```
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If you ever need to know the hook code, use `z.getHook()`:
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```python
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%pyspark
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print z.getHook("post_exec")
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print 'This code should be executed after the paragraph code!'
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```
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Any call to `z.registerHook()` will automatically overwrite what was previously registered.
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To completely unregister a hook event, use `z.unregisterHook(eventCode)`.
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Currently only `"post_exec"` and `"pre_exec"` are valid event codes for the Zeppelin Hook Registry system.
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Finally, the hook registry is internally shared by other interpreters in the same group.
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This would allow for hook code for one interpreter REPL to be set by another as follows:
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```scala
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%spark
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z.unregisterHook("post_exec", "pyspark")
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```
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The API is identical for both the spark (scala) and pyspark (python) implementations.
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### Caveats
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Calls to `z.registerHook("pre_exec", ...)` should be made with care. If there are errors in your specified hook code, this will cause the interpreter REPL to become unable to execute any code pass the pre-execute stage making it impossible for direct calls to `z.unregisterHook()` to take into effect. Current workarounds include calling `z.unregisterHook()` from a different interpreter REPL in the same interpreter group (see above) or manually restarting the interpreter group in the UI.
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