Check for mappings in delete_multi and err out.

Previously, this would cause internal trickery to go wrong and call an
inner function with too many arguments, then fail. The error wouldn't
bubble up either, and a SEGV would ensue.

_pylibmcmodule.c

@@ -859,6 +859,23 @@ static PyObject *PylibMC_Client_delete_multi(PylibMC_Client *self,
                 &keys, &PyInt_Type, &time, &prefix))
         return NULL;
 
+    /**
+     * Because of how DoMulti works, we have to prohibit the use of mappings
+     * here. Otherwise, the values of the mapping will be the second argument
+     * to the delete function; the time argument will then become a third
+     * argument, which delete doesn't take.
+     *
+     * So a mapping to DoMulti would produce calls like:
+     *   DoMulti({"a": 1, "b": 2}, time=3)
+     *      delete("a", 1, 3)
+     *      delete("b", 2, 3)
+     */
+    if (PyMapping_Check(keys)) {
+        PyErr_SetString(PyExc_TypeError,
+            "keys must be a sequence, not a mapping");
+        return NULL;
+    }
+
     if ((delete = PyObject_GetAttrString((PyObject *)self, "delete")) == NULL)
         return NULL;
 
@@ -872,7 +889,10 @@ static PyObject *PylibMC_Client_delete_multi(PylibMC_Client *self,
     }
     Py_DECREF(delete);
 
-    if (PyList_GET_SIZE(retval) == 0) {
+    if (retval == NULL)
+        return NULL;
+
+    if (PyList_Size(retval) == 0) {
         Py_DECREF(retval);
         retval = Py_True;
     } else {

tests.py

@@ -57,6 +57,10 @@ Zero-key-test-time!
 False
 >>> c.set_multi({"": "hi"})
 ['']
+>>> c.delete_multi({"a": "b"})
+Traceback (most recent call last):
+  ...
+TypeError: keys must be a sequence, not a mapping
 
 Timed stuff. The reason we, at UNIX times, set it two seconds in the future and
 then sleep for >3 is that memcached might round the time up and down and left