How do I force Python to be 32-bit on Snow Leopard and other 32-bit/64-bit questions

Question

When I run the following from a bash shell on my Mac:

$ file /usr/bin/python

I get the following three lines:

/usr/bin/python (for architecture x86_64):  Mach-O 64-bit executable x86_64
/usr/bin/python (for architecture i386):    Mach-O executable i386
/usr/bin/python (for architecture ppc7400): Mach-O executable ppc

this would seem to indicate that Python has been compiled for all three architectures or something like that? I believe, based on some errors I had while trying to setup MySQL, that the version I'm using is the 64-bit version. So two questions:

1. How would I have known that?

2. How could I change Python to be 32-bit instead? Something less drastic than re-compile with different compile settings?

3. Why does arch from a bash shell return i386 which would seem to indicate I'm not in "64-bit mode" when I know based on my processor I'm running a 64-bit Mac?

Sorry these are probably all newbie questions, the whole 32/64-bit thing is frustrating the crap out of me and I'm sure there are some commands/tools that would make this easier.

Answer 1

http://www.jaharmi.com/2009/08/29/python_32_bit_execution_on_snow_leopard

$ defaults write com.apple.versioner.python Prefer-32-Bit -bool yes

Answer 2

1. You can find out a lot about the Python version you're running via the platform module (the sys module also has a few simple helpers)

2. On Mac OS X, you can run a "fat binary" with your chosen architecture with, for example,

   arch -i386 /usr/bin/python

I do not recommend altering /usr/lib/python itself (with the lipo command) -- you could easily make your system unusable by tampering with system files. Maybe installing a separate Python from python.org (for application purposes) while leaving the system Python alone is an acceptable strategy to you -- it's definitely safer than altering system files!-)

As for your third question, hmmm, this one's a stumper to me -- and definitely a question for superuser.com (as well as completely unrelated to Python, it also seems completely unrelated to programming;-).

Answer 3

Fix for use with virtualenv on Snow Leopard

danielrsmith's answer works for me when I am not using virtualenv, but virtualenv makes a copy of the python executable which causes it not to work:

$ which python
/Users/cogg/.virtualenvs/tweakeats/bin/python

$ python
[...]
>>> import sys
>>> sys.maxint
9223372036854775807

because this is a copy of python, I used lipo on it to remove the 64-bit architecture. This allows me to use 32-bit python 2.6 with virtualenv:

$ lipo -info /Users/cogg/.virtualenvs/tweakeats/bin/python
Architectures in the fat file: /Users/cogg/.virtualenvs/tweakeats/bin/python are: x86_64 i386 ppc7400
$ mv /Users/cogg/.virtualenvs/tweakeats/bin/python /Users/cogg/.virtualenvs/tweakeats/bin/python.old
$ lipo -remove x86_64 /Users/cogg/.virtualenvs/tweakeats/bin/python.old -output /Users/cogg/.virtualenvs/tweakeats/bin/python
$ python
[...]
>>> import sys
>>> sys.maxint
2147483647