cancel_further_threads.py

import concurrent.futures

def cancel_further_threads(self, futures, number_of_finished_page):
    for fut, page in futures.items():
        if page > number_of_finished_page:
            fut.cancel()
    return futures

test_thredz.py

import unittest
from unittest import mock
import concurrent.futures

from cancel_further_threads import cancel_further_threads

class TestCancelFurtherThreads(unittest.TestCase):
    def test_cancelling_future_threads(self):
        """When a thread comes back with the finished condition(zero api results)-
        then it is time to cancel any later threads currently running.
        Loop through the dict of futures and set to cancel the threads later
        than the finished thread.

        The thread that returns with no results could be right next in line with
        the others that have already finished with full results, or it could be
        several page numbers down the line due to race conditions. For now just
        find the rest of the numbers that the thread finished and cancel the
        later page numbers."""
        sample_futures = {
            concurrent.futures.Future(): page for page in range(0, 7)
        }
        for fut, page in sample_futures.items():
            if page in range(0, 2):
                fut.set_result(pd.DataFrame({'col1': [1, 2], 'col2': [3, 4]}))
            if page == 4:
                fut.set_result(pd.DataFrame())
        number_of_finished_page = 4
        bygone_conclusion_futures = cancel_further_threads(
            sample_futures,
            number_of_finished_page
        )
        for fut, page in bygone_conclusion_futures.items():
            self.assertTrue(fut.done()) if page == 0 else None
            self.assertTrue(fut.done()) if page == 1 else None
            self.assertFalse(fut.done()) if page == 2 else None
            self.assertFalse(fut.done()) if page == 3 else None
            self.assertTrue(fut.done()) if page == 4 else None
            self.assertTrue(fut.cancelled()) if page == 5 else None
            self.assertTrue(fut.cancelled()) if page == 6 else None

The initial idea was that the multithreader would run infinitely until the first thread returned with a finished status, when that occurred it needed a way to cancel any later still running threads.