On Thu, Feb 14, 2019 at 11:38 AM Steve Dower <steve.do...@python.org> wrote:
> As part of adding ARM32 support for Windows, we need to enable > cross-compilation in distutils. This is easy enough, though it requires > somehow getting the target platform as well as the current platform. > > Right now, the change at https://github.com/python/cpython/pull/11774 > adds a get_target_platform() function for this and updates (as far as I > can tell) all uses of get_platform() to use this instead. I would rather > just change get_platform() to return the target platform. > > The current docs are somewhat vague on exactly what this function does, > and I suspect have been mostly written from an "always build from > source" mentality that may have implied, but not explicitly considered > cross-compilation. > > https://docs.python.org/3/distutils/apiref.html#distutils.util.get_platform > > "Return a string that identifies the current platform. This is used > mainly to distinguish platform-specific build directories and > platform-specific built distributions." > > So it says "current" platform, explicitly says that "os.uname()" is the > source, but then goes on to say: > > "For non-POSIX platforms, currently just returns sys.platform." > > Which is incorrect, as sys.platform is always "win32" always but > get_platform() already returns "win-amd64" for 64-bit builds. > > And also: > > "For Mac OS X systems the OS version reflects the minimal version on > which binaries will run (that is, the value of MACOSX_DEPLOYMENT_TARGET > during the build of Python), not the OS version of the current system." > > So it seems like this function is already returning "the default > platform that should be used when building extensions" - ignoring bugs > in libraries that monkeypatch distutils, the "--plat-name" option should > entirely override the return value of this function. > > Given this, does it seem to be okay to have it determine and return the > target platform rather than the host platform? Right now, that would > only affect the new target of building for win-arm32, but I would also > like to update the documentation to make it more about how this value > should be used rather than where it comes from. > > Any objections or concerns? > To alleviate confusion long term I'd love it if we could deprecate the unqualified get_platform() API and point people towards always being explicit about get_target_platform() vs get_current_platform(). There are valid reasons for people to be expecting either target or current return values from get_platform(), but I agree with you, having it return the target platform *feels* more likely to be what people want. It'd be worth auditing a random sample of people's calls of this API in open source projects to confirm that intuition. -gps
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