How can I tell what mode the shell is in, from within the shell?
I’ve tried looking at the platform module, but it seems only to tell you about “the bit architecture and the linkage format used for the executable”. My binary is compiled as 64bit (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.
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Answer
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)
On Windows, run the same commands formatted as follows:
python -c "import sys;print("%x" % sys.maxsize, sys.maxsize > 2**32)"
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