Issue #1445: Fix a SystemError when accessing the cell_contents

amauryfa · amauryfa · commit ce7d10ccc4d0 · 2007-11-24T13:44:17.000Z
attribute of an empty cell object.  Now a ValueError is raised.
diff --git a/Lib/test/test_funcattrs.py b/Lib/test/test_funcattrs.py
@@ -242,6 +242,17 @@ def f(): print a
     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 foo(self): pass
 
 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
@@ -12,6 +12,9 @@ What's New in Python 2.6 alpha 1?
 Core and builtins
 -----------------
 
+- Issue #1445: Fix a SystemError when accessing the ``cell_contents`` 
+  attribute of an empty cell object.
+
 - Issue #1460: The utf-7 incremental decoder did not accept truncated input.
   It now correctly saves its state between chunks of data.
 
diff --git 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;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -89,7 +89,12 @@ cell_clear(PyCellObject *op)`
`89`	`89`	`static PyObject *`
`90`	`90`	`cell_get_contents(PyCellObject op, void closure)`
`91`	`91`	`{`
`92`		`- Py_XINCREF(op->ob_ref);`
	`92`	`+ if (op->ob_ref == NULL)`
	`93`	`+ {`
	`94`	`+ PyErr_SetString(PyExc_ValueError, "Cell is empty");`
	`95`	`+ return NULL;`
	`96`	`+ }`
	`97`	`+ Py_INCREF(op->ob_ref);`
`93`	`98`	`return op->ob_ref;`
`94`	`99`	`}`
`95`	`100`