From 03481c73d119e8c507f06b3aa1097a979501cea5 Mon Sep 17 00:00:00 2001
From: yihong0618 <zouzou0208@gmail.com>
Date: Sun, 12 Oct 2025 16:27:26 +0800
Subject: [PATCH] fix: readline doesn't degrade gracefully when tcsetattr()
 fails.

Signed-off-by: yihong0618 <zouzou0208@gmail.com>
---
 ...025-10-12-16-27-01.gh-issue-139027.Rntwlp.rst |  1 +
 Modules/readline.c                               | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 Misc/NEWS.d/next/macOS/2025-10-12-16-27-01.gh-issue-139027.Rntwlp.rst

diff --git a/Misc/NEWS.d/next/macOS/2025-10-12-16-27-01.gh-issue-139027.Rntwlp.rst b/Misc/NEWS.d/next/macOS/2025-10-12-16-27-01.gh-issue-139027.Rntwlp.rst
new file mode 100644
index 00000000000000..d0fc33f9f5b332
--- /dev/null
+++ b/Misc/NEWS.d/next/macOS/2025-10-12-16-27-01.gh-issue-139027.Rntwlp.rst
@@ -0,0 +1 @@
+Fix: Basic REPL hangs when ioctls can't be written to TTY.
diff --git a/Modules/readline.c b/Modules/readline.c
index 630a6879990949..c83042ed92aeaf 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -17,6 +17,8 @@
 #include <signal.h>               // SIGWINCH
 #include <stdlib.h>               // free()
 #include <string.h>               // strdup()
+#include <termios.h>              // termios, tcgetattr(), tcsetattr()
+#include <unistd.h>               // isatty(), STDIN_FILENO
 #ifdef HAVE_SYS_SELECT_H
 #  include <sys/select.h>         // select()
 #endif
@@ -1645,6 +1647,20 @@ PyInit_readline(void)
     if (mod_state == NULL){
         goto error;
     }
+
+    // gh-139027: If tcsetattr fails do not initialize readline and err it
+    if (isatty(STDIN_FILENO)) {
+        struct termios original_tty;
+        if (tcgetattr(STDIN_FILENO, &original_tty) == 0) {
+            struct termios test_tty = original_tty;
+            if (tcsetattr(STDIN_FILENO, TCSANOW, &test_tty) != 0) {
+                PyErr_SetString(PyExc_OSError,
+                    "termios failure (Operation not permitted)");
+                goto error;
+            }
+        }
+    }
+
     PyOS_ReadlineFunctionPointer = call_readline;
     if (setup_readline(mod_state) < 0) {
         PyErr_NoMemory();