import threading
import random

def hammer_dict(d={}):
    global running
    while running:
        d[key] = 1
        try:
            del d[key]
        except KeyError:
            pass
        except:
            running = False
            raise

class Key:
    def __hash__(self):
        for i in range(random.randint(0, 20)): pass
        print('.', end='')
        return 0
key = Key()
num_threads = 20
threads = [threading.Thread(target=hammer_dict) for x in range(num_threads)]
running = True
for t in threads: t.start()
for t in threads: t.join()