distutils.util.get_platform() semantically differs on (a) Windows and OS X, and on (b) Linux.

Windows/OS X: the return value is derived from the architecture of the *interpreter*, hence for 32-bit Python running on a 64-bit system, get_platform() = 'win32'/'macosx-10.6-i386' (32-bit).

Linux: the return value is derived from the architecture of the *OS*, hence for 32-bit Python running on 64-bit Linux get_platform() = 'linux-x86_64' (64-bit).

Based on a discussion on distutils-sig, the Linux behaviour is probably wrong and should be changed. https://mail.python.org/pipermail/distutils-sig/2013-August/subject.html

My context (where this hit me): I was installing the 32-bit version of the Perforce API (compiled module) on 64-bit Windows and on 64-bit Linux. My command-line was

  python3.3-32 setup.py install --root FOO --install-platlib=lib.$PLAT

(note the '-32' and the '$PLAT')

On Windows, this installed the 32-bit version of the API into "FOO\lib.win32". On Linux, this installed the 64-bit version of the API into "FOO/lib.linux-x86_64".