Python issue 30473

defaultdict_thread.py

import threading
import collections
import datetime
import time


class Test(threading.Thread):
    def run(self):
        # OK!
        dd = collections.defaultdict(lambda: datetime.datetime.now())
        print('works', dd['works'])

        # Boom!
        dd = collections.defaultdict(datetime.datetime.now)
        print('does not work', dd['does not'])


if __name__ == '__main__':
    t = Test()
    t.start()