[Python-Dev] Issue 13524: subprocess on Windows

["Martin v. Löwis"]

> Thoughts?

Apparently, there are at least two "users" of SystemRoot:
- side-by-side (fusion?) apparently uses it to locate the WinSxS
  folder, at least on some Windows releases,
- certain registry keys contain SystemRoot, in particular the
  path names of crypto providers (this apparently is XP only,
  and fixed on Windows 7)

I agree with Nick that we shouldn't do anything except perhaps
for documentation changes. There are many other environment variables
whose absence could also cause failures to run the executable,
such as PATH, LD_LIBRARY_PATH, etc. Even not passing DISPLAY may
cause the subprocess to fail starting.

IOW, users should "normally" pass all environment variables, and
only augment it with any specific additions and deletions that
they know are needed for the subprocess. If a user deliberately
passes a small set of environment variables (e.g. none), we must
assume that it was deliberate, and that any resulting failures
are desired. People do such stuff for security reasons, and
side-stepping their enforcement is not appropriate for Python
to do.

Regards,
Martin