Make isdir/isfile/exists faster on Windows

Author: mdboom

Lib/ntpath.py

@@ -852,11 +852,12 @@ def commonpath(paths):
 
 
 try:
-    # The genericpath.isdir implementation uses os.stat and checks the mode
-    # attribute to tell whether or not the path is a directory.
-    # This is overkill on Windows - just pass the path to GetFileAttributes
+    # The genericpath's isdir and isfile implementations uses os.stat internally.
+    # This is overkill on Windows - just pass the path to GetFileAttributesW
     # and check the attribute from there.
     from nt import _isdir as isdir
+    from nt import _isfile as isfile
+    from nt import _exists as exists
 except ImportError:
-    # Use genericpath.isdir as imported above.
+    # Use genericpath.* as imported above
     pass

Lib/test/test_ntpath.py

@@ -1,3 +1,4 @@
+import inspect
 import ntpath
 import os
 import sys
@@ -889,6 +890,18 @@ def test_isjunction(self):
                 self.assertFalse(ntpath.isjunction('tmpdir'))
                 self.assertPathEqual(ntpath.realpath('testjunc'), ntpath.realpath('tmpdir'))
 
+    @unittest.skipIf(sys.platform != 'win32', "Fast paths are only for win32")
+    def test_fast_paths_in_use(self):
+        # There are fast paths of these functions implemented in posixmodule.c.
+        # Confirm that they are being used, and not the Python fallbacks in
+        # genericpath.py.
+        self.assertTrue(os.path.isdir is nt._isdir)
+        self.assertFalse(inspect.isfunction(os.path.isdir))
+        self.assertTrue(os.path.isfile is nt._isfile)
+        self.assertFalse(inspect.isfunction(os.path.isfile))
+        self.assertTrue(os.path.exists is nt._exists)
+        self.assertFalse(inspect.isfunction(os.path.exists))
+
 
 class NtCommonTest(test_genericpath.CommonTest, unittest.TestCase):
     pathmodule = ntpath

Misc/NEWS.d/next/Windows/2023-01-25-11-33-54.gh-issue-101196.wAX_2g.rst

@@ -0,0 +1,2 @@
+The functions `os.path.isdir`, `os.path.isfile` and `os.path.exists` are now
+13% to 28% faster on Windows, by making fewer win32 API calls.