'can't read "os.subplatform": can't read "os_subplatform": no such variable'

[Joshua Root]

Ryan Schmidt wrote:
> os.subplatform was added to MacPorts in version 1.9.0, back in 2010. It should always be set--to "macosx" if you are running MacPorts on macOS, or to "puredarwin" on any other Darwin variant. It should not be possible for you to encounter this error on macOS...

Unless /System/Library/Frameworks/Carbon.framework is missing.

- Josh