item_24.py

#!/usr/bin/env python3

# Copyright 2014 Brett Slatkin, Pearson Education Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Preamble to mimick book environment
import logging
from pprint import pprint
from sys import stdout as STDOUT


# Example 1
class InputData(object):
    def read(self):
        raise NotImplementedError


# Example 2
class PathInputData(InputData):
    def __init__(self, path):
        super().__init__()
        self.path = path

    def read(self):
        return open(self.path).read()


# Example 3
class Worker(object):
    def __init__(self, input_data):
        self.input_data = input_data
        self.result = None

    def map(self):
        raise NotImplementedError

    def reduce(self, other):
        raise NotImplementedError


# Example 4
class LineCountWorker(Worker):
    def map(self):
        data = self.input_data.read()
        self.result = data.count('\n')

    def reduce(self, other):
        self.result += other.result


# Example 5
import os

def generate_inputs(data_dir):
    for name in os.listdir(data_dir):
        yield PathInputData(os.path.join(data_dir, name))


# Example 6
def create_workers(input_list):
    workers = []
    for input_data in input_list:
        workers.append(LineCountWorker(input_data))
    return workers


# Example 7
from threading import Thread

def execute(workers):
    threads = [Thread(target=w.map) for w in workers]
    for thread in threads: thread.start()
    for thread in threads: thread.join()

    first, rest = workers[0], workers[1:]
    for worker in rest:
        first.reduce(worker)
    return first.result


# Example 8
def mapreduce(data_dir):
    inputs = generate_inputs(data_dir)
    workers = create_workers(inputs)
    return execute(workers)


# Example 9
from tempfile import TemporaryDirectory
import random

def write_test_files(tmpdir):
    for i in range(100):
        with open(os.path.join(tmpdir, str(i)), 'w') as f:
            f.write('\n' * random.randint(0, 100))

with TemporaryDirectory() as tmpdir:
    write_test_files(tmpdir)
    result = mapreduce(tmpdir)

print('There are', result, 'lines')


# Example 10
class GenericInputData(object):
    def read(self):
        raise NotImplementedError

    @classmethod
    def generate_inputs(cls, config):
        raise NotImplementedError


# Example 11
class PathInputData(GenericInputData):
    def __init__(self, path):
        super().__init__()
        self.path = path

    def read(self):
        return open(self.path).read()

    @classmethod
    def generate_inputs(cls, config):
        data_dir = config['data_dir']
        for name in os.listdir(data_dir):
            yield cls(os.path.join(data_dir, name))


# Example 12
class GenericWorker(object):
    def __init__(self, input_data):
        self.input_data = input_data
        self.result = None

    def map(self):
        raise NotImplementedError

    def reduce(self, other):
        raise NotImplementedError

    @classmethod
    def create_workers(cls, input_class, config):
        workers = []
        for input_data in input_class.generate_inputs(config):
            workers.append(cls(input_data))
        return workers


# Example 13
class LineCountWorker(GenericWorker):
    def map(self):
        data = self.input_data.read()
        self.result = data.count('\n')

    def reduce(self, other):
        self.result += other.result


# Example 14
def mapreduce(worker_class, input_class, config):
    workers = worker_class.create_workers(input_class, config)
    return execute(workers)


# Example 15
with TemporaryDirectory() as tmpdir:
    write_test_files(tmpdir)
    config = {'data_dir': tmpdir}
    result = mapreduce(LineCountWorker, PathInputData, config)
print('There are', result, 'lines')