1 files changed, 32 insertions, 0 deletions
diff --git a/Lib/test/crashers/gc_inspection.py b/Lib/test/crashers/gc_inspection.py
new file mode 100644
index 0000000..10caa79
--- /dev/null
+++ b/Lib/test/crashers/gc_inspection.py
@@ -0,0 +1,32 @@
+"""
+gc.get_referrers() can be used to see objects before they are fully built.
+
+Note that this is only an example.  There are many ways to crash Python
+by using gc.get_referrers(), as well as many extension modules (even
+when they are using perfectly documented patterns to build objects).
+
+Identifying and removing all places that expose to the GC a
+partially-built object is a long-term project.  A patch was proposed on
+SF specifically for this example but I consider fixing just this single
+example a bit pointless (#1517042).
+
+A fix would include a whole-scale code review, possibly with an API
+change to decouple object creation and GC registration, and according
+fixes to the documentation for extension module writers.  It's unlikely
+to happen, though.  So this is currently classified as
+"gc.get_referrers() is dangerous, use only for debugging".
+"""
+
+import gc
+
+
+def g():
+    marker = object()
+    yield marker
+    # now the marker is in the tuple being constructed
+    [tup] = [x for x in gc.get_referrers(marker) if type(x) is tuple]
+    print tup
+    print tup[1]
+
+
+tuple(g())