Step 5: Make aq_chain aware of __parent__ pointers.

_Acquisition.c

@@ -1650,7 +1650,7 @@ module_aq_inner(PyObject *ignored, PyObject *args)
 static PyObject *
 capi_aq_chain(PyObject *self, int containment)
 {
-  PyObject *result;
+  PyObject *result, *v, *tb;
 
   UNLESS (result=PyList_New(0)) return NULL;
 
@@ -1673,8 +1673,27 @@ capi_aq_chain(PyObject *self, int containment)
             }
         }
       else
-        if (PyList_Append(result, self) < 0)
-          goto err;
+        {
+          if (PyList_Append(result, self) < 0)
+            goto err;
+
+          if ((self=PyObject_GetAttr(self, py__parent__)))
+            {
+              Py_DECREF(self); /* don't need our own reference */
+              if (self!=Py_None)
+                continue;
+            }
+          else
+            {
+              PyErr_Fetch(&self,&v,&tb);
+              if (self && (self != PyExc_AttributeError))
+                {
+                  PyErr_Restore(self,v,tb);
+                  return NULL;
+                }
+              Py_XDECREF(self); Py_XDECREF(v); Py_XDECREF(tb);
+            }
+        }
 
       break;
     }

tests.py

@@ -1714,7 +1714,10 @@ def test___parent__no_wrappers():
       >>> Acquisition.aq_parent(y) is z
       True
 
-    TODO aq_chain
+    as well as ``aq_chain``:
+
+      >>> Acquisition.aq_chain(x) == [x, y, z]
+      True
     """
 
 def test_implicit_wrapper_as___parent__():
@@ -1767,6 +1770,11 @@ def test_implicit_wrapper_as___parent__():
       >>> Acquisition.aq_parent(y) is z
       True
 
+    as well as ``aq_chain``:
+
+      >>> Acquisition.aq_chain(x) == [x, y, z]
+      True
+
     Note that also the (implicit) acquisition wrapper has a __parent__
     pointer, which is automatically computed from the acquisition
     container (it's identical to aq_parent):
@@ -1791,8 +1799,6 @@ def test_implicit_wrapper_as___parent__():
       Traceback (most recent call last):
         ...
       AttributeError: __parent__
-
-    TODO aq_chain
     """
 
 def test_explicit_wrapper_as___parent__():
@@ -1843,6 +1849,11 @@ def test_explicit_wrapper_as___parent__():
       >>> Acquisition.aq_parent(y) is z
       True
 
+    as well as ``aq_chain``:
+
+      >>> Acquisition.aq_chain(x) == [x, y, z]
+      True
+
     Note that also the (explicit) acquisition wrapper has a __parent__
     pointer, which is automatically computed from the acquisition
     container (it's identical to aq_parent):
@@ -1867,8 +1878,6 @@ def test_explicit_wrapper_as___parent__():
       Traceback (most recent call last):
         ...
       AttributeError: __parent__
-
-    TODO aq_chain
     """
 
 def test_implicit_wrapper_has_nonwrapper_as_aq_parent():
@@ -1917,6 +1926,13 @@ def test_implicit_wrapper_has_nonwrapper_as_aq_parent():
       >>> Acquisition.aq_parent(y) is z
       True
 
+    as well as ``aq_chain``:
+
+      >>> Acquisition.aq_chain(x) == [x, y, z]
+      True
+      >>> x.aq_chain == [x, y, z]
+      True
+
     Because the outmost object, ``x``, is wrapped in an implicit
     acquisition wrapper, we can also use direct attribute access:
 
@@ -1926,8 +1942,6 @@ def test_implicit_wrapper_has_nonwrapper_as_aq_parent():
       42
       >>> x.bar
       3.145
-
-    TODO aq_chain
     """
 
 def test_explicit_wrapper_has_nonwrapper_as_aq_parent():
@@ -1976,7 +1990,12 @@ def test_explicit_wrapper_has_nonwrapper_as_aq_parent():
       >>> Acquisition.aq_parent(y) is z
       True
 
-    TODO aq_chain
+    as well as ``aq_chain``:
+
+      >>> Acquisition.aq_chain(x) == [x, y, z]
+      True
+      >>> x.aq_chain == [x, y, z]
+      True
     """
 
 import unittest