[Python-Dev] Python startup time

[Ray Donnelly]

On Wed, May 2, 2018 at 6:55 PM, Nathaniel Smith <njs at pobox.com> wrote:
> On Wed, May 2, 2018, 09:51 Gregory Szorc <gregory.szorc at gmail.com> wrote:
>>
>> Correct me if I'm wrong, but aren't there downsides with regards to C
>> extension compatibility to not having a shared libpython? Or does all the
>> packaging tooling "just work" without a libpython? (It's possible I have
my
>> wires crossed up with something else regarding a statically linked
Python.)
>
>
> IIRC, the rule on Linux is that if you build an extension on a statically
> built python, then it can be imported on a shared python, but not
> vice-versa. Manylinux wheels are therefore always built on a static python
> so that they'll work everywhere. (We should probably clean this up
upstream
> at some point, but there's not a lot of appetite for touching this stuff –
> very obscure, very easy to break things without realizing it, not much
> upside.)
>
> On Windows I don't think there is such a thing as a static build, because
> extensions have to link to the python dll to work at all. And on MacOS I'm
> not sure, though from knowing how their linker works my guess is that all
> extensions act like static extensions do on Linux.

Yes, on Windows there's always a python?.dll.

macOS is an interesting one. For Anaconda 5.0 I read somewhere (how's that
for a useless reference - and perhaps I got the wrong end of the stick)
that Python for all Unixen should use a statically linked interpreter so I
happily went ahead and did that. Of course I tested it against a good few
wheels at the time and everything seemed fine (well, no worse than the
usual binary compatibility woes at least) so I went ahead with it.

Now that Python 3.7 is around the corner we have a chance to re-evaluate
this decision. We have received no binary compat. bugs whatsoever due to
this change (we got a few bugs where people used python-config incorrectly
either directly or via swig or CMake), were we just lucky?

Anyway, it is obviously safer for us to do what upstream does and I will
try to post some benchmarks of static vs shared to the list so we can
discuss it. I guess it is a little late in the release schedule to propose
any such change for 3.7? If not I will try to prepare something. I will
discuss it in depth with the rest of the AD team soon too.

>
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