From 92de18f3bba696a67699d3cd7043be8559691902 Mon Sep 17 00:00:00 2001
From: David Foster <david@dafoster.net>
Date: Thu, 8 Jan 2026 17:46:26 -0500
Subject: [PATCH 1/2] Fix modutils._is_subpath to handle base with trailing
 os.sep

---
 ChangeLog              |  4 ++++
 astroid/modutils.py    |  6 +++++-
 tests/test_modutils.py | 22 ++++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 0e4312e579..01182a975d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -42,6 +42,10 @@ What's New in astroid 4.0.4?
 ============================
 Release date: TBA
 
+* Fix ability to detect .py modules inside PATH directories on Windows
+  described by a UNC path with a trailing backslash (`\`)
+    - Example: modutils.modpath_from_file(filename=r"\\Mac\Code\tests\test_resources.py", path=["\\mac\code\"]) == ['tests', 'test_resources']
+
 
 
 What's New in astroid 4.0.3?
diff --git a/astroid/modutils.py b/astroid/modutils.py
index 0868c60c0a..acca79cbea 100644
--- a/astroid/modutils.py
+++ b/astroid/modutils.py
@@ -237,7 +237,11 @@ def _is_subpath(path: str, base: str) -> bool:
     base = os.path.normcase(os.path.normpath(base))
     if not path.startswith(base):
         return False
-    return (len(path) == len(base)) or (path[len(base)] == os.path.sep)
+    return (
+        (len(path) == len(base)) or 
+        (path[len(base)] == os.path.sep) or
+        (base.endswith(os.path.sep) and path[len(base) - 1] == os.path.sep)
+    )
 
 
 def _get_relative_base_path(filename: str, path_to_check: str) -> list[str] | None:
diff --git a/tests/test_modutils.py b/tests/test_modutils.py
index 1d6959f11c..ad020a68e5 100644
--- a/tests/test_modutils.py
+++ b/tests/test_modutils.py
@@ -151,6 +151,28 @@ def test_get_module_part_only_dot(self) -> None:
         self.assertEqual(modutils.get_module_part(".", modutils.__file__), ".")
 
 
+
+class IsSubpathTest(unittest.TestCase):
+    """Tests for modutils._is_subpath,
+    which is used internally by modutils.modpath_from_file."""
+
+    @unittest.skipUnless(sys.platform == "win32", "Windows-specific path test")
+    def test_is_subpath_with_trailing_separator_unc_path(self) -> None:
+        self.assertTrue(modutils._is_subpath(
+            "\\\\Mac\\Code\\tests\\test_resources.py",
+            # UNC path with trailing separator
+            "\\\\mac\\code\\"
+        ))
+
+    @unittest.skipUnless(sys.platform == "win32", "Windows-specific path test")
+    def test_is_subpath_without_trailing_separator_unc_path(self) -> None:
+        self.assertTrue(modutils._is_subpath(
+            "\\\\Mac\\Code\\tests\\test_resources.py",
+            # UNC path without trailing separator
+            "\\\\mac\\code"
+        ))
+
+
 class ModPathFromFileTest(unittest.TestCase):
     """Given an absolute file path return the python module's path as a list."""
 

From 2d471d3424a28e744f1cb1e192e6bbedf132e1dc Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 8 Jan 2026 23:06:54 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 astroid/modutils.py    |  6 +++---
 tests/test_modutils.py | 25 ++++++++++++++-----------
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/astroid/modutils.py b/astroid/modutils.py
index acca79cbea..bb2c7c4dde 100644
--- a/astroid/modutils.py
+++ b/astroid/modutils.py
@@ -238,9 +238,9 @@ def _is_subpath(path: str, base: str) -> bool:
     if not path.startswith(base):
         return False
     return (
-        (len(path) == len(base)) or 
-        (path[len(base)] == os.path.sep) or
-        (base.endswith(os.path.sep) and path[len(base) - 1] == os.path.sep)
+        (len(path) == len(base))
+        or (path[len(base)] == os.path.sep)
+        or (base.endswith(os.path.sep) and path[len(base) - 1] == os.path.sep)
     )
 
 
diff --git a/tests/test_modutils.py b/tests/test_modutils.py
index ad020a68e5..f50c535902 100644
--- a/tests/test_modutils.py
+++ b/tests/test_modutils.py
@@ -151,26 +151,29 @@ def test_get_module_part_only_dot(self) -> None:
         self.assertEqual(modutils.get_module_part(".", modutils.__file__), ".")
 
 
-
 class IsSubpathTest(unittest.TestCase):
     """Tests for modutils._is_subpath,
     which is used internally by modutils.modpath_from_file."""
 
     @unittest.skipUnless(sys.platform == "win32", "Windows-specific path test")
     def test_is_subpath_with_trailing_separator_unc_path(self) -> None:
-        self.assertTrue(modutils._is_subpath(
-            "\\\\Mac\\Code\\tests\\test_resources.py",
-            # UNC path with trailing separator
-            "\\\\mac\\code\\"
-        ))
+        self.assertTrue(
+            modutils._is_subpath(
+                "\\\\Mac\\Code\\tests\\test_resources.py",
+                # UNC path with trailing separator
+                "\\\\mac\\code\\",
+            )
+        )
 
     @unittest.skipUnless(sys.platform == "win32", "Windows-specific path test")
     def test_is_subpath_without_trailing_separator_unc_path(self) -> None:
-        self.assertTrue(modutils._is_subpath(
-            "\\\\Mac\\Code\\tests\\test_resources.py",
-            # UNC path without trailing separator
-            "\\\\mac\\code"
-        ))
+        self.assertTrue(
+            modutils._is_subpath(
+                "\\\\Mac\\Code\\tests\\test_resources.py",
+                # UNC path without trailing separator
+                "\\\\mac\\code",
+            )
+        )
 
 
 class ModPathFromFileTest(unittest.TestCase):