Hi, I have run across a puzzling issue in Python, and I wonder if anyone on the list can explain it.
I have a python function which takes some input and produces some output - it doesn't keep permanent state, and presumably running it twice would do exactly the same thing twice, and take exactly the same time. But strangely, it doesn't - the first call takes 14 milliseconds, while the second and all subsequent calls take only 2 milliseconds each. Does anybody have any idea why this can happen? I considered, and discredited, the following attempted "explanations": 1. "The extra 12 milliseconds is the time it takes to read and/or compile the function's code". This explanation isn't true, because the code is read and/or compiled already when I "import" the module, before I measure the first call to the function. Moreover, if I measure parts of this function's code, I see it becomes uniformly slow - e.g., half of its code gets done in 6 milliseconds; It's not a 12 millisecond pause and then the rest of the function finishes in 2ms. 2. "The code is slower the first time it runs, because only then does it get compiled and/or optimized". As far as I know, Python doesn't do JIT so this isn't a correct explanation... 3. "If class A imports B which imports C which imports D, some of these classes are only read when the code is actually used for the first time". Again, I couldn't find any evidence that this is true in Python (unlike, e.g., Java). An "import" would read the whole class hierarchy into memory. Right? Any ideas? Thanks, Nadav. -- Nadav Har'El | Wednesday, Jun 20 2012, n...@math.technion.ac.il |----------------------------------------- Phone +972-523-790466, ICQ 13349191 |I am thinking about a new signature. Stay http://nadav.harel.org.il |tuned. _______________________________________________ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
