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I am trying to compile a package on Mac OSX 10.6.5. The package's install script relies on distutils. The problem is that the computer's default gcc is version 4.2 (I determined this by just running gcc --version in a terminal window) but when I run 'python setup.py build', I see from the output that the distutils is choosing gcc-4.0 instead of 4.2 This is a big problem because the code I am using require gcc >= 4.2. I do not have admin rights on this machine, so as a workaroud, I created some symlinks that send gcc-4.0 to gcc-4.2. The result is the code compiles, but the generated .so files do not work (when I try to import them in python, I get errors complaining about a missing init function in the shared object).

I have tried compiling this code on a different mac (10.6.6) and it works like a charm: distutils chooses 4.2 without being forced to do so and I can import the generated shared object without a problem. So, what I would like to do is to compile the code on my computer without having to do this symlink trickery...I just want distutils to choose 4.2 automatically as it should. I have tried taking the .so files that compile properly and transferring them to my computer, but that fails for a number of reasons (they are linked against libraries that are not present on my machine/are a different version that those installed).

Does anyone have any advice here?

Thanks, Josh

Josh G.
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4 Answers4

19

To force distutils to use a separate compiler, you can redefine a few variables via the environment. First, find out what distutils is using as defaults:

>>> from distutils import sysconfig
>>> sysconfig.get_config_var('LDSHARED')
'gcc-4.0 -Wl,-F. -bundle -undefined dynamic_lookup'
>>> sysconfig.get_config_var('CC')
'gcc-4.0'

Next you need to redefine those, substituting in the version of gcc you'd like to use:

% LDSHARED="gcc-4.2 -Wl,-F. -bundle -undefined dynamic_lookup" CC=gcc-4.2 \
    /usr/bin/python setup.py build_ext

Keep in mind that the sysconfig defaults are pulled from the Makefile which was originally used to compile python, so fudging with them may produce unintended results:

>>> path = sysconfig.get_python_lib(plat_specific=1, standard_lib=1)
>>> os.path.join(path, 'config', 'Makefile')
'/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/config/Makefile'
samplebias
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5

Have you tried setting a custom CC environment variable?

CC=gcc-4.2 python setup.py build
merwok
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3

You don't say which versions of Python you are using but chances are that the default Python on the machine you are using is not the Apple-supplied Python 2.6.1, more likely one installed from python.org. Try running the build script with /usr/bin/python2.6 which should be the Apple-supplied Python 2.6; that does use gcc-4.2.

When you use Python's Distutils (typically by running a setup.py script or using easy_install), Distutils tries to make sure that any C extension modules in the package you are installing will be compiled with the same compiler version and with compatible compilation options (CPU archs, ABI, etc) as was used to build Python itself. Traditionally, most python.org installers for OS X provide a universal Python that works on multiple versions of OS X and multiple CPU archs. That's why they are built with gcc-4.0. If you need to use gcc-4.2 for some other library, then the safest thing is to use a Python that was built with gcc-4.2. The Apple-supplied system Pythons on OS X 10.6 are so built. Also, for the most recent releases of Python (2.7.1 and 3.2), python.org provides a second OS X installer variant for OS X 10.6 that is also built with gcc-4.2. But if you do not have admin access to your machine, that's not an option anyway.

You can see which python is being used by default by:

which python
Ned Deily
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1

You can either adjust your distutils.cfg (see here) or you can pass command line arguments as --compiler=gcc42 (not sure about the last one).

Constantinius
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  • This doesn't seem to work. The valid compiler is just 'gcc'. Throwing in the version doesn't work - it throws an error saying it doesn't know how to build with gcc42. – Josh G. May 11 '11 at 16:10
  • Should probably be `--compiler=gcc-4.2` – cdarke May 11 '11 at 16:11
  • Unfortunately, that still doesn't help. If you check distutils.ccompiler, available options are things like "unix" or "minwg." It doesn't seem to notice things like version. – Josh G. May 11 '11 at 16:25