How do I determine if my python shell is executing in 32bit or 64bit?

Question

I need a way to tell what mode the shell is in from within the shell.

While I'm primarily an OS X user, I'd be interested in knowing about other platforms as well.

I've tried looking at the platform module but it seems only to tell you about "about the bit architecture and the linkage format used for the executable": the binary is compiled as 64bit though (I'm running on OS X 10.6) so it seems to always report 64bit even though I'm using the methods described here to force 32bit mode).

Answer 1

One way is to look at sys.maxsize as documented here:

$ python-32 -c 'import sys;print("%x" % sys.maxsize, sys.maxsize > 2**32)' ('7fffffff', False) $ python-64 -c 'import sys;print("%x" % sys.maxsize, sys.maxsize > 2**32)' ('7fffffffffffffff', True) 

sys.maxsize was introduced in Python 2.6. If you need a test for older systems, this slightly more complicated test should work on all Python 2 and 3 releases:

$ python-32 -c 'import struct;print( 8 * struct.calcsize("P"))' 32 $ python-64 -c 'import struct;print( 8 * struct.calcsize("P"))' 64 

BTW, you might be tempted to use platform.architecture() for this. Unfortunately, its results are not always reliable, particularly in the case of OS X universal binaries.

$ arch -x86_64 /usr/bin/python2.6 -c 'import sys,platform; print platform.architecture()[0], sys.maxsize > 2**32' 64bit True $ arch -i386 /usr/bin/python2.6 -c 'import sys,platform; print platform.architecture()[0], sys.maxsize > 2**32' 64bit False