Eryk Sun added the comment:
Windows Python determines sys.prefix (i.e. the location of the standard
library, <prefix>\lib) via either the PYTHONHOME environment variable or by
searching for the landmark "lib/os.py", starting in the application directory
and reducing back to the root directory [1].
If it can't find the prefix directory; PYTHONPATH isn't defined; and it can't
find PythonPath in the registry; then it adds the "DLLs" and "lib" directories
relative to the working directory. This default PYTHONPATH is defined in
PC/pyconfig.h as ".\\DLLs;.\\lib".
There is an alternative "applocal" (application local) mode. Create a file
named pyvenv.cfg beside python.exe that contains the single line
applocal = true
This prevents Python from checking PYTHONHOME and PYTHONPATH, the registry, and
prevents searching for the "lib/os.py" landmark. sys.prefix is set as the
application directory, and the default "DLLs" and "lib" paths are expanded
relative to the application directory.
Anyway, since what you're reporting is the expected behavior, I'm closing this
issue. Feel free to reopen it if you feel I've misdiagnosed the problem or
think the default behavior is somehow broken. I don't know what Steve Dower's
plans are, if indeed he has any, to change the legacy sys.path behavior in
future releases.
[1]: The reduce() function in PC/getpathp.c has a minor bug that
results in sys.prefix set as the drive-relative path "C:" if
the landmark search continues to the root and "C:/lib/os.py"
exists. This is due to the way it overwrites the path separator
with NUL to reduce the path. I think it should keep the
separator. The join() function works either way.
----------
nosy: +eryksun
resolution: -> not a bug
stage: -> resolved
status: open -> closed
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<https://bugs.python.org/issue27874>
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