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[Python-Dev] Python startup time

Cesare Di Mauro cesare.di.mauro at gmail.com
Thu Jul 20 13:09:38 EDT 2017 
2017-07-19 16:26 GMT+02:00 Victor Stinner <victor.stinner at gmail.com>:

> 2017-07-19 15:22 GMT+02:00 Oleg Broytman <phd at phdru.name>:
> > On Wed, Jul 19, 2017 at 02:59:52PM +0200, Victor Stinner <
> victor.stinner at gmail.com> wrote:
> >> "Python is very slow to start on Windows 7"
> >> https://stackoverflow.com/questions/29997274/python-is-
> very-slow-to-start-on-windows-7
> >
> >    However hard you are going to optimize Python you cannot fix those
> > "defenders", "guards" and "protectors". :-) This particular link can be
> > excluded from consideration.
>
> Sorry, I didn't read carefully each link I posted. Even for me knowing
> what Python does at startup, it's hard to explain why 3 people have
> different timing: 15 ms, 75 ms and 300 ms for example. In my
> experience, the following things impact Python startup:
>
> * -S option: loading or not the site module
> * Paths in sys.path: PYTHONPATH environment variable for example
> * .pth files files in sys.path
> * Python running in a virtual environment or not
> * Operating system: Python loads different modules at startup
> depending on the OS. Naoki INADA just removed _osx_support from being
> imported in the site module on macOS for example.
>
> My list is likely incomplete.
>
> In the performance benchmark suite, a controlled virtual environment
> is created to have a known set of modules. FYI running Python is a
> virtual environment is slower than "system" python which runs outside
> a virtual environment...
>
> Victor
>
> Hi Victor,

I assume that Python loads compiled (.pyc and/or .pyo) from the stdlib.
That's something that also influences the startup time (compiling source vs
loading pre-compiled modules).

Bests,
Cesare

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