[Python-Dev] Wrong OSX platform in sysconfig.py causing installation problems

Sun May 8 01:59:16 EDT 2016

On Fri, May 6, 2016 at 10:43 AM, Joseph Lee Nunn III <josephnunn at gmail.com>
wrote:

> Then I have found the right list to post on, for my problem is a bug in
> the Python 3.5.1 distribution.  Albeit one which will only manifest in
> certain situations.
>
> The presence of numerous `-isysroot /Developer/SDKs/MacOSX10.6.sdk`
> directives in the following file
>
>
> /Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/_sysconfigdata.py
>

As I understand it, that is all there so that when extensions are built,
they are linked against that SDK -- so you can build extensions that can
then be run on any system 10.6 and greater.

> Will cause errors for people who have kept around the old /Developer
> directory tree, and old SDKs like 10.6, for building backwards compatible
> old code.

what are the errors -- wouldn't the old SDK be found, and used, and that's
exactly what's intended?

>   Newer versions of the SDKs are now kept inside the Xcode application
> itself.  And then they will only have a problem when trying to install a
> package with C extensions,

well, sure. of course this is an issue for building C extensions.

> which in my case was Persistence, a dependency of ZODB.  And even more so,
> ONLY when trying to pip install said package into a virtual environment
> created by 3.5’s pyvenv command, if installing the package into the system
> wide Python there will be no error.
>

hmm, As I understand it the building process should be exactly the same
whether you are on a virtualenv or not. but if so -- maybe the "solution"
is to build a wheel outside virtualenv, and then install that wheel in the
virtualenv. But I agree, it should work, of course.

> You see the -isysroot flag has the unusual behavior where instead of
> reporting an error when it cannot find the newly specified system root it
> simply has no effect.  So if you don’t have the SDK specified in the
> location specified then the flag does nothing, as I assume is the case for
> 99% of people.
>

Indeed, that's been working fine for me for a while. However it's this
behavior that is actually the bug -- extensions are supposed to be build
against the 10.6 SDK -- and that's not what's happening in this case

> I understand the need to make Python 3.5 backwards compatible, but doing
> it this way would appear to have the side effect of breaking the ability to
> install packages using C extensions in virtual environments, or at least it
> did for me.
>

It does sound like you've hit a bug, but I actually think you've
misidentified the bug -- I'm trying to understand why it's not working in a
virtualenv -- THAT's the bug.

And I have no idea what to do about it -- thanks Apple for moving things --
that's a great way to keep backward compatibility!

Ned: I'm trying to explore this a bit now (on a 10.9 system), so I followed
the instructions in the Python developers guide, and did:

xcode-select --install

And was a bit surprised that It did a substantial download -- I thought I
already had the XCode command line tools -- but whatever. After running
that, I found I had the 10.9 and 10.10 SDKs (I think that installed the
10.10 one, I previously had only 10.9). And they are buried deep in
XCode.app ....

OK, but how would I go about getting the 10.6 SDK??? This SO post:

http://stackoverflow.com/questions/11989007/where-to-get-macos-sdk-10-6-for-xcode

indicates that it's a serious pain in the $%^% -- thank Apple! But, as far
as I can tell, if you install an old XCode, you will get the older SDKs,
and installed into the old location.

(this is why I kept a 10.6 system around for a long time -- to build python
extensions...)

But what should we do? IF you are building extensions only for yourself,
then I think whatever the heck SDK you have will work fine -- but how to
build for distribution?

.... Trying to decide if I want to go through the hassle of installing an
old XCode to see if i can replicate the bug the OP is reporting....

-CHB

> https://docs.python.org/devguide/setup.html#build-dependencies
>

> >
> > Installing Xcode by itself is not sufficient.  The sysroot and flag
> values you note in _sysconfigdata.py are normal and there for compatibility
> with installing on older versions of OS X; they should not cause a problem
> on newer releases.  For what it's worth, I was able to install ZODB with
> the current python.org 3.5.1 on OS X 10.11.4 using either venv or
> virtualenv.
> >
> > Good luck!
> >
> > --Ned
> >
> > P.S. Mailing list info is available here: https://mail.python.org.  The
> bug tracker is here: https://bugs.python.org
> >
> > --
> >  Ned Deily
> >  nad at python.org -- []
> >
>
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