python · aisk · Apr 28, 2025 · Apr 29, 2025 · Apr 29, 2025 · Apr 29, 2025
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
@@ -2577,6 +2577,14 @@ def test_ftruncate(self):
    def test_lseek(self):
        self.check(os.lseek, 0, 0)

+    @unittest.skipUnless(hasattr(os, 'lseek'), 'test needs os.lseek()')
+    @unittest.skipUnless(hasattr(os, 'pipe'), "need os.pipe()")
+    def test_lseek_on_pipe(self):
+        rfd, wfd = os.pipe()
+        self.addCleanup(os.close, rfd)
+        self.addCleanup(os.close, wfd)
+        self.assertRaises(OSError, os.lseek, rfd, 123, os.SEEK_END)
+
    @unittest.skipUnless(hasattr(os, 'read'), 'test needs os.read()')
    def test_read(self):
        self.check(os.read, 1)

diff --git a/Misc/NEWS.d/next/Windows/2025-04-29-17-55-55.gh-issue-86768.uIDTHc.rst b/Misc/NEWS.d/next/Windows/2025-04-29-17-55-55.gh-issue-86768.uIDTHc.rst
@@ -0,0 +1,2 @@
+:exc:`OSError` will be raised if call :func:`os.lseek` with non seekable
+object on Windows.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
@@ -219,6 +219,7 @@
 #  if defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_SYSTEM)
 #    define HAVE_SYMLINK
 #  endif /* MS_WINDOWS_DESKTOP | MS_WINDOWS_SYSTEM */
+extern int winerror_to_errno(int);
 #endif


@@ -11406,7 +11407,7 @@ static Py_off_t
 os_lseek_impl(PyObject *module, int fd, Py_off_t position, int how)
 /*[clinic end generated code: output=971e1efb6b30bd2f input=f096e754c5367504]*/
 {
-    Py_off_t result;
+    Py_off_t result = 0;

 #ifdef SEEK_SET
    /* Turn 0, 1, 2 into SEEK_{SET,CUR,END} */
@@ -11420,14 +11421,28 @@ os_lseek_impl(PyObject *module, int fd, Py_off_t position, int how)
    Py_BEGIN_ALLOW_THREADS
    _Py_BEGIN_SUPPRESS_IPH
 #ifdef MS_WINDOWS
-    result = _lseeki64(fd, position, how);
+    HANDLE h = (HANDLE)_get_osfhandle(fd);
+    if (h == INVALID_HANDLE_VALUE) {
+        result = -1;
+    }
+    if (result >= 0) {
+        if (GetFileType(h) != FILE_TYPE_DISK) {
+            // Only file is seekable
+            errno = ESPIPE;
+            result = -1;
+        }
+    }
+    if (result >= 0) {
+        result = _lseeki64(fd, position, how);
+    }
 #else
    result = lseek(fd, position, how);
 #endif
    _Py_END_SUPPRESS_IPH
    Py_END_ALLOW_THREADS
-    if (result < 0)
+    if (result < 0) {
        posix_error();
+    }

    return result;
 }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		:exc:`OSError` will be raised if call :func:`os.lseek` with non seekable
		object on Windows.