[Python-Dev] To reduce Python "application" startup time

INADA Naoki songofacandy at gmail.com
Wed Sep 6 00:30:23 EDT 2017

>> This patch moves a few imports inside functions. I wonder whether that kind
>> of change actually helps with real applications—doesn't any real application
>> end up importing the socket module anyway at some point?
> I don't know if this particular change is worthwhile, but one place
> where startup slowness is particularly noticed is with commands like
> 'foo.py --help' or 'foo.py --generate-completions' (the latter called
> implicitly by hitting <tab> in some shell), which typically do lots of
> imports that end up not being used.

Yes. And There are more worse scenario.

1. Jinja2 supports asyncio.  So it imports asyncio.
2. asyncio imports concurrent.futures, for compatibility with Future class.
3. concurrent.futures package does
    `from concurrent.futures.process import ProcessPoolExecutor`
4. concurrent.futures.process package imports multiprocessing.

So when I use Jinja2 but not asyncio or multiprocessing, I need to import
large dependency tree.
I want to make `import asyncio` dependency tree smaller.

FYI, current version of Jinja2 has very large regex which took more than 100ms
when import time.  It is fixed in master branch.  So if you try to see
Jinja2, please
use master branch.


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