From 238a0e11bb4dba6f5357d7ff7890bd6d9c3515ea Mon Sep 17 00:00:00 2001
From: Solaris-star <820622658@qq.com>
Date: Tue, 1 Sep 2026 18:09:31 +0800
Subject: [PATCH] gh-126929: Retry extension loading with long Windows paths

Signed-off-by: Solaris-star <820622658@qq.com>
---
 ...10-05-00.gh-issue-126929.long-path-dll.rst |  1 +
 Python/dynload_win.c                          | 30 +++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Windows/2026-09-01-10-05-00.gh-issue-126929.long-path-dll.rst

diff --git a/Misc/NEWS.d/next/Windows/2026-09-01-10-05-00.gh-issue-126929.long-path-dll.rst b/Misc/NEWS.d/next/Windows/2026-09-01-10-05-00.gh-issue-126929.long-path-dll.rst
new file mode 100644
index 00000000000000..62cd5257c864c9
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2026-09-01-10-05-00.gh-issue-126929.long-path-dll.rst
@@ -0,0 +1 @@
+Fix loading extension modules from long Windows paths by retrying with an extended-length path after the initial load fails and the target is confirmed to be a regular file.
diff --git a/Python/dynload_win.c b/Python/dynload_win.c
index 1c2544e94160ac..77ae331eccf9d4 100644
--- a/Python/dynload_win.c
+++ b/Python/dynload_win.c
@@ -307,6 +307,36 @@ dl_funcptr _PyImport_FindSharedFuncptrWindows(const char *prefix,
         hDLL = LoadLibraryExW(wpathname, NULL,
                               LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
                               LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
+        if (hDLL == NULL) {
+            DWORD attributes = GetFileAttributesW(wpathname);
+            if (attributes != INVALID_FILE_ATTRIBUTES &&
+                !(attributes & FILE_ATTRIBUTE_DIRECTORY)) {
+                size_t path_length = wcslen(wpathname);
+                int is_unc = wpathname[0] == L'\\' && wpathname[1] == L'\\';
+                size_t prefix_length = is_unc ? 8 : 4;
+                wchar_t *extended_path = PyMem_RawMalloc(
+                    (path_length + prefix_length + 1) * sizeof(wchar_t));
+                if (extended_path != NULL) {
+                    if (is_unc) {
+                        wcscpy_s(extended_path, path_length + prefix_length + 1,
+                                 L"\\\\?\\UNC\\");
+                        wcscat_s(extended_path, path_length + prefix_length + 1,
+                                 wpathname + 2);
+                    }
+                    else {
+                        wcscpy_s(extended_path, path_length + prefix_length + 1,
+                                 L"\\\\?\\");
+                        wcscat_s(extended_path, path_length + prefix_length + 1,
+                                 wpathname);
+                    }
+                    hDLL = LoadLibraryExW(
+                        extended_path, NULL,
+                        LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
+                        LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
+                    PyMem_RawFree(extended_path);
+                }
+            }
+        }
         Py_END_ALLOW_THREADS
         PyMem_Free(wpathname);