calculate pi using python generator.

pi_generator.py

#!/usr/bin/env python

def pi():
  # Wallis' product
  numerator = 2.0
  denominator = 1.0
  while True:
    yield numerator/denominator
    if numerator < denominator:
      numerator += 2
    else:
      denominator += 2

p = pi()

res = 1.0
for i in range(10000000):
  res *= next(p)

print res * 2