On Tue, Mar 8, 2016 at 12:34 PM, Steven D'Aprano <st...@pearwood.info> wrote: > On Tue, 8 Mar 2016 07:47 am, Chris Angelico wrote: > >> You write *real world* code and then profile that. You get actual real >> programs that you actually really use, and you run those through >> timing harnesses. > > > Chris, I think that's exactly what BartC has done: he has a program that he > actually uses, one which processes JPG files. It's written in pure Python, > so he's not comparing the quality of C libraries, he's comparing Python > versus Python.
The trouble is that we can't be sure _what_ he's done. All we have is that it takes longer under some circumstances than others. Without knowing a lot more about how the measurements are done, I don't know that we can get anything from it. And I remember seeing a performance analysis that showed that array.array() actually sucks for performance; hence my recommendation to try other ways of doing things, before saying "Python 3 is slower than Python 2". > Could Bart's code be improved for production use? Almost certainly. I'm sure > that by using a C image processing library, like pillow, it would be ten or > a hundred times faster. If Bart were saying "Python is crap, it's too slow" > then a perfectly acceptable response would be "no, you're just misusing it, > here you want to use it as an interface to this library and let the library > do the heavy lifting". That's what Python is designed for. But that's not > what Bart is saying. > > I'm impressed that pure Python code running in CPython is even *usable* for > whatever sort of image processing BartC is doing. He must be doing > something right, given that its not unusably slow. Fair point. Although these are only small files (as far as I know), so even if there's an O(N**2) memory allocation (eg with a naive "take a byte off the front and give me back the rest" algorithm), it'd quite probably still be usable. I've had N Squareds in code that sat there until the day I did some stupid benchmark on a gig of data, and only then started seeing problems. Readably-written code isn't necessarily that much slower than tightly-optimized code. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
