From: Amaury Forgeot d'Arc <amauryfa@gmail.com>
Date: Sat, 24 Nov 2007 13:53:29 +0000 (+0000)
Subject: Issue #1445: Fix a SystemError when accessing the ``cell_contents``
X-Git-Tag: v2.5.2c1~118
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=30f61cbb1331615af829aea69d2586e990488525;p=python

Issue #1445: Fix a SystemError when accessing the ``cell_contents``
attribute of an empty cell object.  Now a ValueError is raised.

Backport of r59170.
---

diff --git a/Lib/test/test_funcattrs.py b/Lib/test/test_funcattrs.py
index 7a083b70df..a32be38333 100644
--- a/Lib/test/test_funcattrs.py
+++ b/Lib/test/test_funcattrs.py
@@ -242,6 +242,17 @@ def test_func_closure():
     verify(c[0].__class__.__name__ == "cell") # don't have a type object handy
     cantset(f, "func_closure", c)
 
+def test_empty_cell():
+    def f(): print a
+    try:
+        f.func_closure[0].cell_contents
+    except ValueError:
+        pass
+    else:
+        raise TestFailed, "shouldn't be able to read an empty cell"
+
+    a = 12
+
 def test_func_doc():
     def f(): pass
     verify(f.__doc__ is None)
@@ -385,6 +396,7 @@ def test_im_name():
 
 def testmore():
     test_func_closure()
+    test_empty_cell()
     test_func_doc()
     test_func_globals()
     test_func_name()
diff --git a/Misc/NEWS b/Misc/NEWS
index c633032e5b..f856c1f29b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -1,4 +1,4 @@
-+++++++++++
++++++++++++
 Python News
 +++++++++++
 
@@ -12,6 +12,9 @@ What's New in Python 2.5.2c1?
 Core and builtins
 -----------------
 
+- Issue #1445: Fix a SystemError when accessing the ``cell_contents`` 
+  attribute of an empty cell object.
+
 - Issue #1265: Fix a problem with sys.settrace, if the tracing function uses a
   generator expression when at the same time the executed code is closing a
   paused generator.
diff --git a/Objects/cellobject.c b/Objects/cellobject.c
index 65a29aaca8..e659555f56 100644
--- a/Objects/cellobject.c
+++ b/Objects/cellobject.c
@@ -89,7 +89,12 @@ cell_clear(PyCellObject *op)
 static PyObject *
 cell_get_contents(PyCellObject *op, void *closure)
 {
-	Py_XINCREF(op->ob_ref);
+	if (op->ob_ref == NULL)
+	{
+		PyErr_SetString(PyExc_ValueError, "Cell is empty");
+		return NULL;
+	}
+	Py_INCREF(op->ob_ref);
 	return op->ob_ref;
 }