Generators in python

generator.py

#!/usr/bin/python2.6

import random

# yields a random customer id
def random_generator(percentage):
  for customer in xrange(1000000):
    if random.randrange(0, 100, 1) < percentage:
      yield customer

# generates a bunch of random user ids and unpaid customers
customers = (customer for customer in random_generator(70))
unpaid_customers = (unpaid for unpaid in random_generator(10))

# parse by only looking at first item of unpaid customers
# O(1) vs O(n) for unpaid_customers
# O(n) vs O(n2) for global lookup
# does not load the whole list in memory
match = 0 
current_id = -1
for customer_id in customers:
  if unpaid_customers:
    if customer_id >= current_id:
      try:
        current_id = unpaid_customers.next()
      except StopIteration, error:
        break
      if customer_id == current_id:
        match += 1

print '%d matches.' % match