Calculate Pi using the Monte Carlo method. Happy Pi Day!

pi_monte_carlo.py

# Calculate Pi via the Monte Carlo method
# Throw darts at a square region and count how many fall into a
# quarter-circle.  The ratio of that count to the total number of darts
# is 1/4 * Pi!
# More information (and a cool graphic) here:
# http://en.wikipedia.org/wiki/Monte_Carlo_method
#
# A classroom project by KidsCanCode - http://kidscancode.org/
from random import random
import math
from time import time

# How many darts to throw?  The more darts, the more accurate the estimate
# (but the longer it will take)
num_darts = 100000

# Let's time how long it takes
start = time()
hits = 0
for i in range(num_darts):
    # Pick a random location in a square area
    x, y = random(), random()
    # See if the dart is inside the quarter-circle
    # x^2 + y^2 = 1 is the formula for a circle
    if x*x + y*y <= 1:
        hits += 1

# calculate Pi!
pi_calculated = 4 * hits / num_darts
# Let's also see how close we were
accuracy = 100 * (math.pi - pi_calculated) / math.pi
print("Time: %.3f sec" % (time() - start))
print("Pi (estimated): %.6f (Accuracy: %.4f%%)" % (pi_calculated, accuracy))