gh-85681: Make ntpath.abspath() platform independent

On Windows the path normalization strips trailing dots and spaces from the
last component of the path, and a single trailing dot from other components.
abspath() on other platforms now does the same, so relpath() and other
functions based on it no longer depend on the platform.

Author: serhiy-storchaka

Lib/ntpath.py

@@ -516,6 +516,26 @@ def normpath(path):
     from nt import _getfullpathname
 
 except ImportError: # not running on Windows - mock up something sensible
+    def _strip_dots_and_spaces(path):
+        # As the Windows path normalization does.
+        if isinstance(path, bytes):
+            sep = b'\\'
+            dot = b'.'
+            dots_and_spaces = b'. '
+        else:
+            sep = '\\'
+            dot = '.'
+            dots_and_spaces = '. '
+        drive, root, tail = splitroot(path)
+        if not tail:
+            return path
+        comps = tail.split(sep)
+        for i, comp in enumerate(comps[:-1]):
+            if len(comp) > 1 and comp.endswith(dot) and not comp.endswith(dot*2):
+                comps[i] = comp[:-1]
+        comps[-1] = comps[-1].rstrip(dots_and_spaces)
+        return drive + root + sep.join(comps)
+
     def abspath(path):
         """Return the absolute version of a path."""
         path = os.fspath(path)
@@ -525,7 +545,7 @@ def abspath(path):
             else:
                 cwd = os.getcwd()
             path = join(cwd, path)
-        return normpath(path)
+        return _strip_dots_and_spaces(normpath(path))
 
 else:  # use native Windows method on Windows
     def abspath(path):

Lib/test/test_ntpath.py

@@ -1210,6 +1210,35 @@ def test_expanduser(self):
 
 
 
+    def test_abspath_dots_and_spaces(self):
+        # gh-85681: trailing dots and spaces are stripped from the last
+        # component, and a single trailing dot from other components.
+        tester('ntpath.abspath("C:/spam. . .")', "C:\\spam")
+        tester('ntpath.abspath("C:/spam.")', "C:\\spam")
+        tester('ntpath.abspath("C:/spam ")', "C:\\spam")
+        tester('ntpath.abspath("C:/spam..")', "C:\\spam")
+        tester('ntpath.abspath("C:/.spam")', "C:\\.spam")
+        tester('ntpath.abspath("C:/spam./eggs")', "C:\\spam\\eggs")
+        tester('ntpath.abspath("C:/spam.b./eggs")', "C:\\spam.b\\eggs")
+        tester('ntpath.abspath("C:/spam ./eggs")', "C:\\spam \\eggs")
+        # A trailing dot preceded by a dot is not stripped.
+        tester('ntpath.abspath("C:/spam../eggs")', "C:\\spam..\\eggs")
+        tester('ntpath.abspath("C:/spam.../eggs")', "C:\\spam...\\eggs")
+        # Trailing dots and spaces are stripped even in extended paths.
+        tester('ntpath.abspath("\\\\?\\C:/spam. . .")', "\\\\?\\C:\\spam")
+        tester('ntpath.abspath("\\\\.\\C:/spam. . .")', "\\\\.\\C:\\spam")
+        tester('ntpath.abspath("//server/share/spam. ")',
+               "\\\\server\\share\\spam")
+
+    def test_relpath_dots_and_spaces(self):
+        # gh-85681: relpath() is based on abspath().
+        tester('ntpath.relpath("foo ", "foo")', ".")
+        tester('ntpath.relpath("foo.", "foo")', ".")
+        tester('ntpath.relpath("foo/bar ", "foo")', "bar")
+        tester('ntpath.relpath("foo/bar.", "foo")', "bar")
+        # "foo.." denotes "foo" as the last component, but not as other.
+        tester('ntpath.relpath("foo../bar", "foo..")', "..\\foo..\\bar")
+
     @unittest.skipUnless(nt, "abspath requires 'nt' module")
     def test_abspath(self):
         tester('ntpath.abspath("C:\\")', "C:\\")

Misc/NEWS.d/next/Library/2026-08-08-23-30-00.gh-issue-85681.ntabs.rst

@@ -0,0 +1,3 @@
+:func:`ntpath.abspath` on non-Windows platforms now strips trailing dots and
+spaces like the Windows path normalization does.  This makes
+:func:`ntpath.relpath` and other functions based on it platform independent.