Django Mulitprocessing with Progress Bar

December 10, 2018

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Instead of rolling my own progress bars on new batch management commands, I've been using tqdm lately. Here's a quick snippet for multiprocessing a batch of items in a queryset.

You'll need tqdm to run this: pip install tqdm

Note: Since the function that I'm calling is using django's ORM, I close all db connections. Things tend to go wrong when forked processes are all using the same connection.

from django.db import connection
from django.core.management.base import BaseCommand

from multiprocessing import Pool
from tqdm import tqdm

from project.models import Item

def func(item):
    connection.close()
    # Do some process
    return True


class Command(BaseCommand):

    def add_arguments(self, parser):
        parser.add_argument(
            '--processes',
            dest='processes',
            default=2,
            type=int,
            help='Number of processes to use to make run command on queryset',
        )

    def handle(self, *args, **options):
        items = Item.objects.all()

        with tqdm(total=items.count()) as bar, Pool(processes=options['processes']) as pool:
            for _ in pool.imap_unordered(func, items):
                bar.update()