π — calculated by chance

monte_pi.py

from random import random
import multiprocessing
from datetime import datetime

def run_simulation(throws=1000000):
    hits = 0
    count = 0
    while count < throws:
        count += 1
        x = random()
        y = random()
        distance = (x ** 2 + y ** 2) ** 0.5
        hits += distance <= 1
    return hits


if __name__ == '__main__':
    start = datetime.now()
    print "Starting simulation..."
    pool = multiprocessing.Pool()
    throws = 1000000000 # 1.000.000.000 throws
    tasks = [throws / multiprocessing.cpu_count()] * multiprocessing.cpu_count()
    r = pool.map_async(run_simulation, tasks)
    hits = sum(r.get())
    print "Pi, calculated by chance: ", 4 * (hits / float(throws))
    print "Time: ", datetime.now() - start