Nov 9, 2025 · Nov 2, 2025
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
                         'socket.if_indextoname() not available.')
    @support.skip_android_selinux('if_indextoname')
    def testInvalidInterfaceIndexToName(self):
        self.assertRaises(OSError, socket.if_indextoname, 0)
        with self.assertRaises(OSError) as cm:
            socket.if_indextoname(0)
        self.assertIsNotNone(cm.exception.errno)

        self.assertRaises(ValueError, socket.if_indextoname, -1)
        self.assertRaises(OverflowError, socket.if_indextoname, 2**1000)
        self.assertRaises(TypeError, socket.if_indextoname, '_DEADBEEF')
                         'socket.if_nametoindex() not available.')
    @support.skip_android_selinux('if_nametoindex')
    def testInvalidInterfaceNameToIndex(self):
        with self.assertRaises(OSError) as cm:
            socket.if_nametoindex("_DEADBEEF")
        self.assertIsNotNone(cm.exception.errno)

        self.assertRaises(TypeError, socket.if_nametoindex, 0)
        self.assertRaises(OSError, socket.if_nametoindex, '_DEADBEEF')

    @unittest.skipUnless(hasattr(sys, 'getrefcount'),
                         'test needs sys.getrefcount()')
diff --git a/Misc/NEWS.d/next/Library/2025-11-02-11-46-00.gh-issue-100218.9Ezfdq.rst b/Misc/NEWS.d/next/Library/2025-11-02-11-46-00.gh-issue-100218.9Ezfdq.rst
 Correctly set :attr:`~OSError.errno` when :func:`socket.if_nametoindex` or
 :func:`socket.if_indextoname` raise an :exc:`OSError`. Patch by Bénédikt
 Tran.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
    unsigned long index;
 #endif

    errno = ENODEV;  // in case 'if_nametoindex' does not set errno
    index = if_nametoindex(PyBytes_AS_STRING(oname));
    if (index == 0) {
        /* if_nametoindex() doesn't set errno */
        PyErr_SetString(PyExc_OSError, "no interface with this name");
        PyErr_SetFromErrno(PyExc_OSError);
        return NULL;
    }

 _socket_if_indextoname_impl(PyObject *module, NET_IFINDEX index)
 /*[clinic end generated code: output=e48bc324993052e0 input=c93f753d0cf6d7d1]*/
 {
    errno = ENXIO;  // in case 'if_indextoname' does not set errno
    char name[IF_NAMESIZE + 1];
    if (if_indextoname(index, name) == NULL) {
        PyErr_SetFromErrno(PyExc_OSError);
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1176,7 +1176,10 @@ def testInterfaceNameIndex(self):
		'socket.if_indextoname() not available.')
		@support.skip_android_selinux('if_indextoname')
		def testInvalidInterfaceIndexToName(self):
		self.assertRaises(OSError, socket.if_indextoname, 0)
		with self.assertRaises(OSError) as cm:
		socket.if_indextoname(0)
		self.assertIsNotNone(cm.exception.errno)

		self.assertRaises(ValueError, socket.if_indextoname, -1)
		self.assertRaises(OverflowError, socket.if_indextoname, 2**1000)
		self.assertRaises(TypeError, socket.if_indextoname, '_DEADBEEF')
Expand All		@@ -1196,8 +1199,11 @@ def testInvalidInterfaceIndexToName(self):
		'socket.if_nametoindex() not available.')
		@support.skip_android_selinux('if_nametoindex')
		def testInvalidInterfaceNameToIndex(self):
		with self.assertRaises(OSError) as cm:
		socket.if_nametoindex("_DEADBEEF")
		self.assertIsNotNone(cm.exception.errno)

		self.assertRaises(TypeError, socket.if_nametoindex, 0)
		self.assertRaises(OSError, socket.if_nametoindex, '_DEADBEEF')

		@unittest.skipUnless(hasattr(sys, 'getrefcount'),
		'test needs sys.getrefcount()')
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Correctly set :attr:`~OSError.errno` when :func:`socket.if_nametoindex` or
		:func:`socket.if_indextoname` raise an :exc:`OSError`. Patch by Bénédikt
		Tran.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -7294,10 +7294,10 @@ _socket_if_nametoindex_impl(PyObject module, PyObject oname)
		unsigned long index;
		#endif

		errno = ENODEV; // in case 'if_nametoindex' does not set errno
		index = if_nametoindex(PyBytes_AS_STRING(oname));
		if (index == 0) {
		/* if_nametoindex() doesn't set errno */
		PyErr_SetString(PyExc_OSError, "no interface with this name");
		PyErr_SetFromErrno(PyExc_OSError);
		return NULL;
		}

Expand All		@@ -7317,6 +7317,7 @@ static PyObject *
		_socket_if_indextoname_impl(PyObject *module, NET_IFINDEX index)
		/[clinic end generated code: output=e48bc324993052e0 input=c93f753d0cf6d7d1]/
		{
		errno = ENXIO; // in case 'if_indextoname' does not set errno
		char name[IF_NAMESIZE + 1];
		if (if_indextoname(index, name) == NULL) {
		PyErr_SetFromErrno(PyExc_OSError);
Expand Down