[Python-Dev] Python startup optimization: script vs. service

[Brett Cannon]

On Mon, 2 Oct 2017 at 08:00 Christian Heimes <christian at python.org> wrote:

> On 2017-10-02 15:26, Victor Stinner wrote:
> > 2017-10-02 13:10 GMT+02:00 INADA Naoki <songofacandy at gmail.com>:
> >> https://github.com/python/cpython/pull/3796
> >> In this PR, lazy loading only happens when uuid1 is used.
> >> But uuid1 is very uncommon for nowdays.
> >
> > Antoine Pitrou added a new C extension _uuid which is imported as soon
> > as uuid(.py) is imported. On Linux at least, the main "overhead" is
> > still done on "import uuid". But Antoine change optimized a lot
> > "import uuid" import time!
> >
> >> https://github.com/python/cpython/pull/3757
> >> In this PR, singledispatch is lazy loading types and weakref.
> >> But singledispatch is used as decorator.
> >> So if web application uses singledispatch, it's loaded before
> preforking.
> >
> > While "import module" is fast, maybe we should use sometimes a global
> > variable to cache the import.
> >
> > module = None
> > def func():
> >    global module
> >    if module is None: import module
> >    ...
> >
> > I'm not sure that it's possible to write an helper for such pattern.
>
> I would rather like to see a function in importlib that handles deferred
> imports:
>
> modulename = importlib.deferred_import('modulename')
>
> def deferred_import(name):
>     if name in sys.modules:
>         # special case 'None' here
>         return sys.modules[name]
>     else:
>         return ModuleProxy(name)
>
> ModuleProxy is a module type subclass that loads the module on demand.
>

My current design for an opt-in lazy importing setup includes an explicit
function for importlib that's mainly targeted for the stdlib and it's
startup module needs, but could be used by others:
https://notebooks.azure.com/Brett/libraries/di2Btqj7zSI/html/Lazy%20importing.ipynb
.
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