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Python native implementation of the Spark RDD interface.

Project description

pysparkling

A native Python implementation of Spark’s RDD interface, but instead of being resilient and distributed it is just transient and local; but fast (lower latency than PySpark). It is a drop in replacement for PySpark’s SparkContext and RDD.

Use case: you have a pipeline that processes 100k input documents and converts them to normalized features. They are used to train a local scikit-learn classifier. The preprocessing is perfect for a full Spark task. Now, you want to use this trained classifier in an API endpoint. You need the same pre-processing pipeline for a single document per API call. This does not have to be done in parallel, but there should be only a small overhead in initialization and preferably no dependency on the JVM. This is where pysparkling shines.

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Features

  • Parallelization via multiprocessing.Pool, concurrent.futures.ThreadPoolExecutor or any other Pool-like objects that have a map(func, iterable) method.
  • AWS S3 is supported. Use file paths of the form s3n://bucket_name/filename.txt with Context.textFile(). Specify multiple files separated by comma. Use environment variables AWS_SECRET_ACCESS_KEY and AWS_ACCESS_KEY_ID for auth. Mixed local and S3 files are supported. Glob expressions (filenames with * and ?) are resolved.
  • Lazy execution is in development.
  • Seamless handling of compressed files is not supported yet.
  • only dependency: boto for AWS S3 access

Examples

Count the lines in the *.py files in the tests directory:

import pysparkling

context = pysparkling.Context()
print(context.textFile('tests/*.py').count())

API

Context

  • __init__(pool=None): takes a pool object (an object that has a map() method, e.g. a multiprocessing.Pool) to parallelize all map() and foreach() methods.
  • textFile(filename): load every line of a text file into a RDD. filename can contain a comma separated list of many files, ? and * wildcards, file paths on S3 (s3n://bucket_name/filename.txt) and local file paths (relative/path/my_text.txt, /absolut/path/my_text.txt or file:///absolute/file/path.txt). If the filename points to a folder containing part* files, those are resolved.
  • broadcast(var): returns an instance of Broadcast() and it’s values are accessed with value.

RDD

  • cache(): execute previous steps and cache result
  • coalesce(): do nothing
  • collect(): return the underlying list
  • count(): get length of internal list
  • countApprox(): same as count()
  • countByKey: input is list of pairs, returns a dictionary
  • countByValue: input is a list, returns a dictionary
  • context(): return the context
  • distinct(): returns a new RDD containing the distinct elements
  • filter(func): return new RDD filtered with func
  • first(): return first element
  • flatMap(func): return a new RDD of a flattened map
  • flatMapValues(func): return new RDD
  • fold(zeroValue, op): aggregate elements
  • foldByKey(zeroValue, op): aggregate elements by key
  • foreach(func): apply func to every element in place
  • foreachPartition(func): same as foreach()
  • groupBy(func): group by the output of func
  • groupByKey(): group by key where the RDD is of type [(key, value), …]
  • histogram(buckets): buckets can be a list or an int
  • id(): currently just returns None
  • intersection(other): return a new RDD with the intersection
  • isCheckpointed(): returns False
  • join(other): join
  • keyBy(func): creates tuple in new RDD
  • keys(): returns the keys of tuples in new RDD
  • leftOuterJoin(other): left outer join
  • lookup(key): return list of values for this key
  • TODO: continue going through the list
  • map(func): apply func to every element and return a new RDD
  • mapValues(func): apply func to value in (key, value) pairs and return a new RDD
  • max(): get the maximum element
  • min(): get the minimum element
  • reduce(): reduce
  • reduceByKey(): reduce by key and return the new RDD
  • rightOuterJoin(other): right outer join
  • take(n): get the first n elements
  • takeSample(n): get n random samples

Broadcast

  • value: access the value it stores

Changelog

Project details


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