whatsnew: os.path.ismount recognizes volumes mounted below root.

Doc/library/os.path.rst

@@ -194,10 +194,16 @@ the :mod:`glob` module.)
 .. function:: ismount(path)
 
    Return ``True`` if pathname *path* is a :dfn:`mount point`: a point in a file
-   system where a different file system has been mounted.  The function checks
+   system where a different file system has been mounted.  On POSIX, the function checks
    whether *path*'s parent, :file:`path/..`, is on a different device than *path*,
    or whether :file:`path/..` and *path* point to the same i-node on the same
    device --- this should detect mount points for all Unix and POSIX variants.
+   On Windows, a drive letter root and a share UNC are always mount
+   points, and for any other path ``GetVolumePathName`` is called to see if it
+   is different from the input path.
+
+   .. versionadded:: 3.4
+      Support for detecting non-root mount points on Windows.
 
 
 .. function:: join(path1[, path2[, ...]])

Doc/whatsnew/3.4.rst

@@ -960,6 +960,9 @@ Chaudhari, Victor Stinner, and Charles-François Natali in :issue:`17914`.)
 :func:`os.path.samefile` implementation is now shared between Unix and
 Windows).  (Contributed by Brian Curtin in :issue:`11939`.)
 
+:func:`os.path.ismount` now recognizes volumes mounted below a drive
+root on Windows. (Contributed by Tim Golden in :issue:`9035`.)
+
 
 pdb
 ---