[Python-Dev] Python startup time (original) (raw)

Ray Donnelly mingw.android at gmail.com
Thu May 3 20:21:54 EDT 2018

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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