=============
External sort

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External sort algorithm implementation. External sorting is a class of sorting algorithms that can handle massive amounts of data. External sorting is required when the data being sorted do not fit into the main memory (RAM) of a computer and instead must be resided in slower external memory, usually a hard disk drive. Sorting is achieved in two passes. During the first pass it sorts chunks of data that each fit in RAM, during the second pass it merges the sorted chunks together. For more information see https://en.wikipedia.org/wiki/External_sorting.

Features

• Uses reader abstraction as a data source so that data can be read from a file/socket/database or any other source
  that implements reader protocol.
• Uses writer abstraction as a sorting result destination so that the result can be written to a file/socket/database
  or any other destination that implements writer protocol.
• Uses python process pool to sort data chunks so that real sorting parallelism can be achieved.
• Uses Serializer and Deserializer abstraction to load/dump data items from/to file so that items of any type
  can be sorted (bytes, strings, numbers, pickled types and so on).

Compatibility

ext-sort requires 3.6+.

Installation

You can install ext-sort with pip:

.. code-block:: console

$ pip install ext-sort

Quick start

Quick start.

.. code-block:: python

import csv
import io
import logging

import ext_sort as es


class CSVSerializer(es.Serializer):

    def __init__(self, writer):
        super().__init__(csv.writer(io.TextIOWrapper(writer, write_through=True)))

    def write(self, item):
        return self._writer.writerow(item)


class CSVDeserializer(es.Deserializer):

    def __init__(self, reader):
        super().__init__(csv.reader(io.TextIOWrapper(reader)))

    def read(self):
        return next(self._reader)


logging.basicConfig(
    level=logging.DEBUG,
    format='[%(levelname)-8s] %(asctime)-15s (%(name)s): %(message)s',
)

with open('/home/user/data.csv', 'rb') as unsorted_file, open('/home/user/data.sorted.csv', 'wb') as sorted_file:
    # save the csv header
    sorted_file.write(unsorted_file.readline())

    es.sort(
        reader=unsorted_file,
        writer=sorted_file,
        chunk_size=10_000_000,
        Serializer=CSVSerializer,
        Deserializer=CSVDeserializer,
        workers_cnt=4,
    )