When iterating over a sequence of numbers in Python, the range() function is commonly used. However, the implementation of the range() function in Python 2.x instantiates each element in the sequence before the iteration begins. This is really costly from both memory and CPU perspectives when the desired range of numbers is large. Consider using the xrange() function instead which implements a Python generator to yield each number in the sequence as needed. Using xrange() instead of range() for large iterations can have a big, positive impact on your code. For example, in an application I was working on recently, replacing range() calls with xrange() boosted my performance from ~900,000 transactions per second to over 3,000,000. In Python 3.x, the range() function is supposed to be implemented as a generator but I haven't tested that to be true yet. Let me know if you have.

I spoke at the Charlottesville .NET User Group this week and at the Raleigh Code Camp. I cheated and did the same presentation to both groups. Call me lazy but, in the middle of planning our own Code Camp in Richmond, I really didn't want to prepare two separate talks. I did a talk back at CodeStock 2009 on a similar topic back in June 2009 but it's evolved a lot since then based on my own growth and understanding. You can find the code and slides below.