EP 24 Use `@classmethod` Polymorphism to Construct Objects Generically ref: http://qiita.com/giwa/items/fd563a93825714cffd70

file0.txt

import os
from threading import Thread

class InputData:
    def read(self):
        raise NotImplementedError

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

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

class Worker:
    def __init__(self, input_data):
        self.input_data = input_data
        self.result = None

    def map(self):
        raise NotImplementedError

    def reduce(self):
        raise NotImplementedError

class LineCountWoker(Worker):
    def map(self):
        data = self.input_data.read()
        self.result = data.count('\n')

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

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

def create_worker(input_list):
    workers = []
    for input_data in input_list:
        workers.append(LineCountWoker(input_data))
    return workers


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 workers in rest:
        first.reduce(worker)
    return first.result

def mapreduce(data_dir):
    inputs = generate_inputs(data_dir)
    workers = create_worker(inputs)
    return execute(workers)


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

file1.txt

import os
from threading import Thread

class GenericInputData:
    def read(self):
        raise NotImplementedError

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

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))

class GenericWorker:
    def __init__(self, input_data):
        self.input_data = input_data
        self.result = None

    def map(self):
        raise NotImplementedError

    def reduce(self):
        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

class LineCountWoker(GenericWorker):
    def map(self):
        data = self.input_data.read()
        self.result = data.count('\n')

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

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

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 workers in rest:
        first.reduce(worker)
    return first.result


with TemporaryDirectory() as tmpdir:
    write_test_files(tmpdir)
    config = {'data_dir': tmpdir}
    result = mapreduce(LineCountWoker, PathInputData, config)

file2.txt

shape.Draw()