Fix bad bug in structseq slicing (NULL pointers in result). Reported by

Jack Jansen on python-dev.
Add simple test case.
Move vereq() from test_descr to test_support (it's handy!).

Lib/test/test_descr.py

 # Test enhancements related to descriptors and new-style classes
 
-from test_support import verify, verbose, TestFailed, TESTFN
+from test_support import verify, vereq, verbose, TestFailed, TESTFN
 from copy import deepcopy
 
-def vereq(a, b):
-    if not (a == b):
-        raise TestFailed, "%r == %r" % (a, b)
-
 def veris(a, b):
     if a is not b:
         raise TestFailed, "%r is %r" % (a, b)

Lib/test/test_structseq.py

+from test_support import vereq
+
+import time
+
+t = time.gmtime()
+astuple = tuple(t)
+vereq(len(t), len(astuple))
+vereq(t, astuple)
+
+# Check that slicing works the same way; at one point, slicing t[i:j] with
+# 0 < i < j could produce NULLs in the result.
+for i in range(-len(t), len(t)):
+    for j in range(-len(t), len(t)):
+        vereq(t[i:j], astuple[i:j])
+
+XXX more needed

Lib/test/test_support.py

@@ -117,6 +117,10 @@ def verify(condition, reason='test failed'):
     if not condition:
         raise TestFailed(reason)
 
+def vereq(a, b):
+    if not (a == b):
+        raise TestFailed, "%r == %r" % (a, b)
+
 def sortdict(dict):
     "Like repr(dict), but in sorted order."
     items = dict.items()

Objects/structseq.c

@@ -75,7 +75,7 @@ structseq_slice(PyStructSequence *obj, int low, int high)
 	for(i = low; i < high; ++i) {
 		PyObject *v = obj->ob_item[i];
 		Py_INCREF(v);
-		PyTuple_SET_ITEM(np, i, v);
+		PyTuple_SET_ITEM(np, i-low, v);
 	}
 	return (PyObject *) np;
 }