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For more information: in 3.0, os.curdir, os.pardir, os.sep, os.altsep,
os.pathsep, os.defpath, and os.devnull are also in os.path. Only
os.extset was removed from os. Among the sysinfo constants, only
os.linesep was not in os.path. I think either all names or none should
be duplicated.
The doc for os.path begins "This module implements some useful functions
on pathnames". The duplication of the sysinfo constants is not
mentioned! (Though perhaps is should be "Also, as a convenience, the
system information constants from os are available here also.") So if
they are only in one place, it should be os, not os.path.
In any case, the removal of extpath and only that from os is gratuitous
breakage.