When I create a virtualenv, python runs in 64-bit even when already set to 32-bit in OSX

Question

My setup is: 2.6.1 python (apple default, snow leopard), virtualenv, and using virtualenvwrapper

Outside the environment, everything runs in 32-bit which is fine. But with a new project I'm going to work on needs django 1.3 and tons of dependencies, so I made a virtualenv.

I've managed to install everything well, except that mysql-python (via pip) gets an error of "mach -o wrong architecture". I've checked my python interpreter with "import sys; sys.maxint" inside the virtualenv and python runs in 64-bit.

I've already set systemwide for python to run in 32-bit via "defaults write com.apple.versioner.python Prefer-32-Bit -bool yes"

Does anyone know why this happens inside the virtualenv?

Answer 1

Much of the "magic" that Apple used to implement their Prefer-32-bit for the system Pythons in OS X 10.6 is in /usr/bin/python which then calls the real Python interpreters which are symlinked at /usr/bin/python2.6 and /usr/bin/python2.5 . virtualenv copies the real interpreter into the virtualenv bin directory so the Prefer-32-bit processing is bypassed.

Among the options to ensure 32-bit operation:

1. Use the arch command to invoke the interpreter.

    $ virtualenv -p /usr/bin/python2.6./p $./p/bin/python -c 'import sys;print(sys.maxsize)' 9223372036854775807 $ arch -i386./p/bin/python -c 'import sys;print(sys.maxsize)' 2147483647

2. Use lipo to extract only the 32-bit arch from the universal binary.

    $ file./p/bin/python./p/bin/python: Mach-O universal binary with 3 architectures./p/bin/python (for architecture x86_64): Mach-O 64-bit executable x86_64./p/bin/python (for architecture i386): Mach-O executable i386./p/bin/python (for architecture ppc7400): Mach-O executable ppc $ cp./p/bin/python./p/bin/python-universal $ lipo./p/bin/python-universal -thin i386 -output./p/bin/python $ file./p/bin/python./p/bin/python: Mach-O executable i386 $./p/bin/python -c 'import sys;print(sys.maxsize)' 2147483647

3. Install and use a newer 32-bit-only Python 2.6 or 2.7 (installers available from python.org )