python · vladima · Dec 19, 2018 · Dec 19, 2018 · Dec 19, 2018 · Dec 20, 2018
diff --git a/Lib/ntpath.py b/Lib/ntpath.py
@@ -527,8 +527,6 @@ def abspath(path):
         except (OSError, ValueError):
             return _abspath_fallback(path)
 
-# realpath is a no-op on systems without islink support
-realpath = abspath
 # Win9x family and earlier have no Unicode filename support.
 supports_unicode_filenames = (hasattr(sys, "getwindowsversion") and
                               sys.getwindowsversion()[3] >= 2)
@@ -640,23 +638,65 @@ def commonpath(paths):
         genericpath._check_arg_types('commonpath', *paths)
         raise
 
+MAX_PATH = 260
 
-# determine if two files are in fact the same file
 try:
-    # GetFinalPathNameByHandle is available starting with Windows 6.0.
-    # Windows XP and non-Windows OS'es will mock _getfinalpathname.
-    if sys.getwindowsversion()[:2] >= (6, 0):
-        from nt import _getfinalpathname
-    else:
-        raise ImportError
-except (AttributeError, ImportError):
-    # On Windows XP and earlier, two files are the same if their absolute
-    # pathnames are the same.
-    # Non-Windows operating systems fake this method with an XP
-    # approximation.
-    def _getfinalpathname(f):
-        return normcase(abspath(f))
+    from nt import _getfinalpathname
+
+    # determine if two files are in fact the same file
+    def realpath(filename):
+        filename = os.fspath(filename)
+        is_str = isinstance(filename, str)
+        if not is_str:
+            filename = os.fsdecode(filename)
+        extended_path_prefix = '\\\\?\\'
+        is_extended_path = filename.startswith(extended_path_prefix)
+        unresolved = filename if is_extended_path else abspath(filename)
+        resolved_parts = []
+        while True:
+            try:
+                resolved_parts.append(_getfinalpathname(unresolved))
+                break
+            except OSError:
+                unresolved, tail = split(unresolved)
+                if not tail:
+                    resolved_parts.append(unresolved)
+                    break
+                resolved_parts.append(tail)
+        resolved = join(*reversed(resolved_parts))
+        # try to convert extended path to normal if
+        # initial path did not use \\?\ prefix and result uses it
+        if not is_extended_path and resolved.startswith(extended_path_prefix):
+            resolved = _extended_to_normal(resolved)
+        return resolved if is_str else os.fsencode(resolved)
+
+    def _extended_to_normal(path):
+        letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+        if path[5:7] == ":\\" and path[4].upper() in letters:
+            # extended path with \\?\ prefix
+            # 4 is len('\\?\')
+            normal_path = normpath(path[4:])
+        elif path[:8].upper() == '\\\\?\\UNC\\':
+            # UNC path with \\?\ prefix - drop prefix
+            # 7 is len('\\?\UNC')
+            normal_path = normpath('\\' + path[7:])
+        else:
+            # not a UNC or drive-letter path
+            # return path as-is
+            return path
 
+        if (len(normal_path) < MAX_PATH and
+            normal_path == _getfullpathname(normal_path)):
+            return normal_path
+        return path
+except ImportError:
+    def realpath(filename):
+        filename = os.fspath(filename)
+        extended_path_prefix = (
+            '\\\\?\\' if isinstance(filename, str) else b'\\\\?\\'
+        )
+        is_extended_path = filename.startswith(extended_path_prefix)
+        return filename if is_extended_path else abspath(filename)
 
 try:
     # The genericpath.isdir implementation uses os.stat and checks the mode

diff --git a/Lib/test/test_ntpath.py b/Lib/test/test_ntpath.py
@@ -5,7 +5,7 @@
 import warnings
 from test.support import TestFailed, FakePath
 from test import support, test_genericpath
-from tempfile import TemporaryFile
+from tempfile import TemporaryFile, TemporaryDirectory
 
 try:
     import nt
@@ -14,6 +14,12 @@
     # but for those that require it we import here.
     nt = None
 
+try:
+    import _winapi
+except ImportError:
+    # realpath tests require _winapi
+    _winapi = None
+
 def tester(fn, wantResult):
     fn = fn.replace("\\", "\\\\")
     gotResult = eval(fn)
@@ -277,6 +283,52 @@ def test_expanduser(self):
             tester('ntpath.expanduser("~/foo/bar")',
                    'C:\\idle\\eric/foo/bar')
 
+    @unittest.skipUnless(nt and _winapi, "realpath requires 'nt' and '_winapi' modules")
+    def test_realpath(self):
+        def to_unc(p):
+            drive, rest = ntpath.splitdrive(file2)
+            return ntpath.join(f"\\\\localhost\\{drive[0]}$", rest)
+        def s2b(s):
+            return bytes(s, "utf-8")
+
+        with TemporaryDirectory() as d:
+            f = ntpath.join(d, "f")
+            os.mkdir(f)
+            f2 = ntpath.join(d, "g")
+            _winapi.CreateJunction(f, f2)
+            try:
+                # realpath for original path and junction is the same
+                self.assertEqualCI(ntpath.realpath(f), ntpath.realpath(f2))
+                self.assertEqualCI(ntpath.realpath(s2b(f)), ntpath.realpath(s2b(f2)))
+
+                # realpath for UNC path is the same
+                file = ntpath.join(f, "file1")
+                open(file, "w+").close()
+                file2 = ntpath.join(f2, "file1")
+                unc1 = to_unc(file)
+                unc2 = to_unc(file2)
+                self.assertEqualCI(ntpath.realpath(unc1), ntpath.realpath(unc2))
+                self.assertEqualCI(ntpath.realpath(s2b(unc1)), ntpath.realpath(s2b(unc2)))
+
+                # realpath for non-existent file F in symlinked folder
+                # is original folder + F
+                file = ntpath.join(f, "missing")
+                file2 = ntpath.join(f2, "missing")
+                self.assertEqualCI(ntpath.realpath(file), ntpath.realpath(file2))
+                self.assertEqualCI(ntpath.realpath(s2b(file)), ntpath.realpath(s2b(file2)))
+
+                # realpath for short names used for non 8.3 directory names
+                dir = ntpath.join(f, "somelongname")
+                os.mkdir(dir)
+                file = ntpath.join(dir, "f")
+                open(file, "w+").close()
+                file_in_f2 = ntpath.join(f2, "somelo~1", "f")
+                self.assertEqualCI(ntpath.realpath(file), ntpath.realpath(file_in_f2))
+                self.assertEqualCI(ntpath.realpath(s2b(file)), ntpath.realpath(s2b(file_in_f2)))
+            finally:
+                os.unlink(f2)
+
+
     @unittest.skipUnless(nt, "abspath requires 'nt' module")
     def test_abspath(self):
         tester('ntpath.abspath("C:\\")', "C:\\")

diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py
@@ -1756,7 +1756,7 @@ def test_move_dangling_symlink(self):
         self.assertTrue(os.path.islink(dst_link))
         # On Windows, os.path.realpath does not follow symlinks (issue #9949)
         if os.name == 'nt':
-            self.assertEqual(os.path.realpath(src), os.readlink(dst_link))
+            self.assertEqual(os.path.realpath(src), os.path.realpath(os.readlink(dst_link)))
         else:
             self.assertEqual(os.path.realpath(src), os.path.realpath(dst_link))
 

diff --git a/Misc/NEWS.d/next/Library/2018-12-19-15-26-35.bpo-14094.8Hotek.rst b/Misc/NEWS.d/next/Library/2018-12-19-15-26-35.bpo-14094.8Hotek.rst
@@ -0,0 +1 @@
+ntpath.realpath() now uses ``GetFinalPathNameByHandle()``.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		ntpath.realpath() now uses ``GetFinalPathNameByHandle()``.