#3242: fix a crash in "print", if sys.stdout is set to a custom object,

whose write() method installs another sys.stdout.

Will backport.

Lib/test/test_file.py

@@ -503,13 +503,31 @@ class FileThreadingTests(unittest.TestCase):
         self._test_close_open_io(io_func)
 
 
+class StdoutTests(unittest.TestCase):
+
+    def test_move_stdout_on_write(self):
+        # Issue 3242: sys.stdout can be replaced (and freed) during a
+        # print statement; prevent a segfault in this case
+        save_stdout = sys.stdout
+
+        class File:
+            def write(self, data):
+                if '\n' in data:
+                    sys.stdout = save_stdout
+
+        try:
+            sys.stdout = File()
+            print "some text"
+        finally:
+            sys.stdout = save_stdout
+
 
 def test_main():
     # Historically, these tests have been sloppy about removing TESTFN.
     # So get rid of it no matter what.
     try:
         run_unittest(AutoFileTests, OtherFileTests, FileSubclassTests,
-            FileThreadingTests)
+            FileThreadingTests, StdoutTests)
     finally:
         if os.path.exists(TESTFN):
             os.unlink(TESTFN)

Misc/NEWS

@@ -10,6 +10,10 @@ What's New in Python 2.6 beta 2?
 Core and Builtins
 -----------------
 
+- Issue #3242: Fix a crash inside the print statement, if sys.stdout is
+  set to a custom object whose write() method happens to install
+  another file in sys.stdout.
+
 - Issue #3088: Corrected a race condition in classes derived from
   threading.local: the first member set by a thread could be saved in
   another thread's dictionary.

Python/ceval.c

@@ -1617,9 +1617,11 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 							"lost sys.stdout");
 			}
 			if (w != NULL) {
+				Py_INCREF(w);
 				err = PyFile_WriteString("\n", w);
 				if (err == 0)
 					PyFile_SoftSpace(w, 0);
+				Py_DECREF(w);
 			}
 			Py_XDECREF(stream);
 			stream = NULL;