On Wed, Mar 16, 2011 at 7:32 PM, Shane O'Connor <spiderbabym...@gmail.com>wrote:
> Hi, > > First-time poster here. I've a question about loop efficiency - I was > wondering whether this code: > > i = 0 > while i < 1000: > do something > i+=1 > > is more efficient than: > > for i in range(1000): > do something > > or: > > for i in xrange(1000): > do something > > In my mind, the while loop should not allocate as much memory as range or > have the overhead of the iterator of xrange (although aesthetically, I > prefer the x/range style). Is this the case or does the compiler do > something clever here? > > In particular, I'm using Python 2.4.3 on a web server which needs to run as > fast as possible using as little memory as possible (no surprises there!). > I'm aware that there are more significant optimizations than the above and I > will profile the code rather than prematurely optimize loops at the sake of > readability/errors but I'm still curious about the answer. > Well, I'm not sure about the xrange v while loop, but I'm 100% certain that range is the least efficient of all - because you both create the iterator *and* a list to iterate over it. My guess is that xrange v while is fairly similar, I do know that the for loop raises/catches a StopIteration under the hood, so there may be some performance issues - I don't think you'll get a big gain unless you're running the loop thousands+ times, but I could be wrong. HTH, Wayne
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