Added type checks to get better error messages.

src/BTrees/BTreeTemplate.c

@@ -1001,6 +1001,12 @@ _BTree_setstate(BTree *self, PyObject *state, int noval)
     if (!PyArg_ParseTuple(state, "O|O:__setstate__", &items, &firstbucket))
 	return -1;
 
+    if (!PyTuple_Check(items)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "tuple required for first state element");
+	return -1;
+    }
+
     len = PyTuple_Size(items);
     if (len < 0)
 	return -1;

src/BTrees/BucketTemplate.c

@@ -1182,6 +1182,12 @@ _bucket_setstate(Bucket *self, PyObject *state)
     if (!PyArg_ParseTuple(state, "O|O:__setstate__", &items, &next))
 	return -1;
 
+    if (!PyTuple_Check(items)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "tuple required for first state element");
+	return -1;
+    }
+
     len = PyTuple_Size(items);
     if (len < 0)
 	return -1;

src/BTrees/SetTemplate.c

@@ -108,6 +108,12 @@ _set_setstate(Bucket *self, PyObject *args)
   UNLESS (PyArg_ParseTuple(args, "O|O", &items, &next))
     return -1;
 
+  if (!PyTuple_Check(items)) {
+    PyErr_SetString(PyExc_TypeError,
+                    "tuple required for first state element");
+    return -1;
+  }
+
   if ((l=PyTuple_Size(items)) < 0) return -1;
 
   for (i=self->len; --i >= 0; )

src/BTrees/tests/testBTrees.py

@@ -83,6 +83,13 @@ class Base(TestCase):
             self._closeRoot(root)
             self._closeRoot(root2)
 
+    def testSetstateArgumentChecking(self):
+        try: self.t.__class__().__setstate__(('',))
+        except TypeError, v:
+            self.assertEqual(str(v), 'tuple required for first state element')
+        else:
+            raise AssertionError("Expected exception")
+
     def testGhostUnghost(self):
         for i in 0, 10, 1000:
             t = self.t.__class__()