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Learn how to use Python in alive MapReduce operations. Hadoop provides a alive API for MapReduce that enables you to address map and abate functions in languages added than Java. The accomplish in this certificate apparatus the Map and Abate apparatus in Python.
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python - What does if __name__ == "__main__": do? - Stack Overflow | python if __name__ __main__A Linux-based Hadoop on HDInsight cluster
Important
The accomplish in this certificate crave an HDInsight array that uses Linux. Linux is the alone operating arrangement acclimated on HDInsight adaptation 3.4 or greater. For added information, see HDInsight retirement on Windows.
A argument editor
Important
The argument editor charge use LF as the band ending. Application a band catastrophe of CRLF causes errors back alive the MapReduce job on Linux-based HDInsight clusters.
The ssh and scp commands, or Azure PowerShell
This archetype is a basal chat calculation implemented in a python a mapper and reducer. The mapper break sentences into alone words, and the reducer aggregates the words and counts to aftermath the output.
The afterward flowchart illustrates what happens during the map and abate phases.
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Use of if __name__ == “__main__”: in Python – a tryst with programming | python if __name__ __main__Hadoop allows you to specify a book that contains the map and abate argumentation that is acclimated by a job. The specific requirements for the map and abate argumentation are:
Python can calmly handle these requirements by application the sys bore to apprehend from STDIN and application book to book to STDOUT. The actual assignment is artlessly formatting the abstracts with a tab (t) appearance amid the key and value.
Create a book called mapper.py and use the afterward cipher as the content:
Create a book called reducer.py and use the afterward cipher as the content:
To ensure that your files accept the appropriate band endings, use the afterward PowerShell script:
Use the afterward PowerShell calligraphy to upload the files, run the job, and appearance the output:
From your development environment, in the aforementioned agenda as mapper.py and reducer.py files, use the afterward command:
Replace username with the SSH user name for your cluster, and clustername with the name of your cluster.
["1241.6"]
Python Tutorial: if __name__ == '__main__' - YouTube | python if __name__ __main__This command copies the files from the bounded arrangement to the arch node.
Note
If you acclimated a countersign to defended your SSH account, you are prompted for the password. If you acclimated an SSH key, you may accept to use the -i constant and the aisle to the clandestine key. For example, scp -i /path/to/private/key mapper.py reducer.py username@clustername-ssh.azurehdinsight.net:.
Connect to the array by application SSH:
For added advice on, see Use SSH with HDInsight.
To ensure the mapper.py and reducer.py accept the actual band endings, use the afterward commands:
Use the afterward command to alpha the MapReduce job.
This command has the afterward parts:
hadoop-streaming.jar: Acclimated back assuming alive MapReduce operations. It interfaces Hadoop with the alien MapReduce cipher you provide.
["1587.89"]
What is if __name__ == '__main__' ? – Trishna Guha | python if __name__ __main__-files: Adds the defined files to the MapReduce job.
-mapper: Tells Hadoop which book to use as the mapper.
-reducer: Tells Hadoop which book to use as the reducer.
-input: The ascribe book that we should calculation words from.
-output: The agenda that the achievement is accounting to.
As the MapReduce job works, the action is displayed as percentages.
15/02/05 19:01:04 INFO mapreduce.Job: map 0% abate 0% 15/02/05 19:01:16 INFO mapreduce.Job: map 100% abate 0% 15/02/05 19:01:27 INFO mapreduce.Job: map 100% abate 100%
To appearance the output, use the afterward command:
This command displays a account of words and how abounding times the chat occurred.
["627.59"]
Use of if __name__ == “__main__”: in Python – a tryst with programming | python if __name__ __main__Now that you accept abstruse how to use alive MapRedcue jobs with HDInsight, use the afterward links to analyze added means to assignment with Azure HDInsight.
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