diff --git a/Objects/listobject.c b/Objects/listobject.c
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -22,8 +22,11 @@
  * Note that self->ob_item may change, and even if newsize is less
  * than ob_size on entry.
  */
+
+#define list_resize(self, newsize) list_resize2(self, newsize, 1)
+
 static int
-list_resize(PyListObject *self, Py_ssize_t newsize)
+list_resize2(PyListObject *self, Py_ssize_t newsize, int keep_overallocated)
 {
     PyObject **items;
     size_t new_allocated;
@@ -33,7 +36,7 @@
        to accommodate the newsize.  If the newsize falls lower than half
        the allocated size, then proceed with the realloc() to shrink the list.
     */
-    if (allocated >= newsize && newsize >= (allocated >> 1)) {
+    if (allocated >= newsize && (keep_overallocated || newsize >= (allocated >> 1))) {
         assert(self->ob_item != NULL || newsize == 0);
         Py_SIZE(self) = newsize;
         return 0;
@@ -2318,6 +2321,42 @@
     return PyLong_FromSsize_t(res);
 }
 
+static PyObject *
+list_preallocate(PyListObject *self, PyObject *v)
+{
+    Py_ssize_t i, new_allocated;
+    PyObject **items;
+
+    i = PyNumber_AsSsize_t(v, PyExc_ValueError);
+    if (i == -1 && PyErr_Occurred())
+        return NULL;
+    if (i <= 0) {
+        PyErr_SetString(PyExc_ValueError,
+                        "size <= 0");
+        return NULL;
+    }
+
+    new_allocated = self->allocated + i;
+    if (new_allocated > (PY_SIZE_MAX / sizeof(PyObject *))) {
+        PyErr_NoMemory();
+        return NULL;
+    }
+
+    items = self->ob_item;
+    PyMem_RESIZE(items, PyObject *, new_allocated);
+    self->ob_item = items;
+    self->allocated = new_allocated;
+    Py_RETURN_NONE;
+}
+
+static PyObject *
+list_shrink(PyListObject *self)
+{
+    list_resize2(self, Py_SIZE(self), 0); /* can't fail */
+    Py_RETURN_NONE;
+}
+
+
 static PyObject *list_iter(PyObject *seq);
 static PyObject *list_reversed(PyListObject* seq, PyObject* unused);
 
@@ -2327,6 +2366,10 @@
 "L.__reversed__() -- return a reverse iterator over the list");
 PyDoc_STRVAR(sizeof_doc,
 "L.__sizeof__() -- size of L in memory, in bytes");
+PyDoc_STRVAR(preallocate_doc,
+"L.__preallocate__(size) -- preallocate slots");
+PyDoc_STRVAR(shrink_doc,
+"L.__shrink__() -- shrink slots");
 PyDoc_STRVAR(clear_doc,
 "L.clear() -> None -- remove all items from L");
 PyDoc_STRVAR(copy_doc,
@@ -2359,6 +2402,8 @@
     {"__getitem__", (PyCFunction)list_subscript, METH_O|METH_COEXIST, getitem_doc},
     {"__reversed__",(PyCFunction)list_reversed, METH_NOARGS, reversed_doc},
     {"__sizeof__",  (PyCFunction)list_sizeof, METH_NOARGS, sizeof_doc},
+    {"__preallocate__", (PyCFunction)list_preallocate, METH_O, preallocate_doc},
+    {"__shrink__",      (PyCFunction)list_shrink, METH_NOARGS, shrink_doc},
     {"clear",           (PyCFunction)listclear,   METH_NOARGS, clear_doc},
     {"copy",            (PyCFunction)listcopy,   METH_NOARGS, copy_doc},
     {"append",          (PyCFunction)listappend,  METH_O, append_doc},
diff --git a/Objects/listobject.c b/Objects/listobject.c
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -22,8 +22,9 @@
  * Note that self->ob_item may change, and even if newsize is less
  * than ob_size on entry.
  */
+
 static int
-list_resize(PyListObject *self, Py_ssize_t newsize)
+list_resize(PyListObject *self, Py_ssize_t newsize, int keep_overallocated)
 {
     PyObject **items;
     size_t new_allocated;
@@ -33,7 +34,7 @@
        to accommodate the newsize.  If the newsize falls lower than half
        the allocated size, then proceed with the realloc() to shrink the list.
     */
-    if (allocated >= newsize && newsize >= (allocated >> 1)) {
+    if (allocated >= newsize && (keep_overallocated || newsize >= (allocated >> 1))) {
         assert(self->ob_item != NULL || newsize == 0);
         Py_SIZE(self) = newsize;
         return 0;
@@ -251,7 +252,7 @@
         return -1;
     }
 
-    if (list_resize(self, n+1) == -1)
+    if (list_resize(self, n+1, 1) == -1)
         return -1;
 
     if (where < 0) {
@@ -291,7 +292,7 @@
         return -1;
     }
 
-    if (list_resize(self, n+1) == -1)
+    if (list_resize(self, n+1, 1) == -1)
         return -1;
 
     Py_INCREF(v);
@@ -646,12 +647,12 @@
     if (d < 0) { /* Delete -d items */
         memmove(&item[ihigh+d], &item[ihigh],
             (Py_SIZE(a) - ihigh)*sizeof(PyObject *));
-        list_resize(a, Py_SIZE(a) + d);
+        list_resize(a, Py_SIZE(a) + d, 0);
         item = a->ob_item;
     }
     else if (d > 0) { /* Insert d items */
         k = Py_SIZE(a);
-        if (list_resize(a, k+d) < 0)
+        if (list_resize(a, k+d, 0) < 0)
             goto Error;
         item = a->ob_item;
         memmove(&item[ihigh+d], &item[ihigh],
@@ -706,7 +707,7 @@
         return PyErr_NoMemory();
     }
 
-    if (list_resize(self, size*n) == -1)
+    if (list_resize(self, size*n, 0) == -1)
         return NULL;
 
     p = size;
@@ -799,7 +800,7 @@
             Py_RETURN_NONE;
         }
         m = Py_SIZE(self);
-        if (list_resize(self, m + n) == -1) {
+        if (list_resize(self, m + n, 0) == -1) {
             Py_DECREF(b);
             return NULL;
         }
@@ -835,7 +836,7 @@
     mn = m + n;
     if (mn >= m) {
         /* Make room. */
-        if (list_resize(self, mn) == -1)
+        if (list_resize(self, mn, 0) == -1)
             goto error;
         /* Make the list sane again. */
         Py_SIZE(self) = m;
@@ -872,7 +873,7 @@
 
     /* Cut back result list if initial guess was too large. */
     if (Py_SIZE(self) < self->allocated)
-        list_resize(self, Py_SIZE(self));  /* shrinking can't fail */
+        list_resize(self, Py_SIZE(self), 0);  /* shrinking can't fail */
 
     Py_DECREF(it);
     Py_RETURN_NONE;
@@ -924,7 +925,7 @@
     }
     v = self->ob_item[i];
     if (i == Py_SIZE(self) - 1) {
-        status = list_resize(self, Py_SIZE(self) - 1);
+        status = list_resize(self, Py_SIZE(self) - 1, 0);
         assert(status >= 0);
         return v; /* and v now owns the reference the list had */
     }
@@ -2318,6 +2319,42 @@
     return PyLong_FromSsize_t(res);
 }
 
+static PyObject *
+list_preallocate(PyListObject *self, PyObject *v)
+{
+    Py_ssize_t i, new_allocated;
+    PyObject **items;
+
+    i = PyNumber_AsSsize_t(v, PyExc_ValueError);
+    if (i == -1 && PyErr_Occurred())
+        return NULL;
+    if (i <= 0) {
+        PyErr_SetString(PyExc_ValueError,
+                        "size <= 0");
+        return NULL;
+    }
+
+    new_allocated = self->allocated + i;
+    if (new_allocated > (PY_SIZE_MAX / sizeof(PyObject *))) {
+        PyErr_NoMemory();
+        return NULL;
+    }
+
+    items = self->ob_item;
+    PyMem_RESIZE(items, PyObject *, new_allocated);
+    self->ob_item = items;
+    self->allocated = new_allocated;
+    Py_RETURN_NONE;
+}
+
+static PyObject *
+list_shrink(PyListObject *self)
+{
+    list_resize(self, Py_SIZE(self), 0);  /* shrinking can't fail */
+    Py_RETURN_NONE;
+}
+
+
 static PyObject *list_iter(PyObject *seq);
 static PyObject *list_reversed(PyListObject* seq, PyObject* unused);
 
@@ -2327,6 +2364,10 @@
 "L.__reversed__() -- return a reverse iterator over the list");
 PyDoc_STRVAR(sizeof_doc,
 "L.__sizeof__() -- size of L in memory, in bytes");
+PyDoc_STRVAR(preallocate_doc,
+"L.__preallocate__(size) -- preallocate slots");
+PyDoc_STRVAR(shrink_doc,
+"L.__shrink__() -- shrink slots");
 PyDoc_STRVAR(clear_doc,
 "L.clear() -> None -- remove all items from L");
 PyDoc_STRVAR(copy_doc,
@@ -2359,6 +2400,8 @@
     {"__getitem__", (PyCFunction)list_subscript, METH_O|METH_COEXIST, getitem_doc},
     {"__reversed__",(PyCFunction)list_reversed, METH_NOARGS, reversed_doc},
     {"__sizeof__",  (PyCFunction)list_sizeof, METH_NOARGS, sizeof_doc},
+    {"__preallocate__", (PyCFunction)list_preallocate, METH_O, preallocate_doc},
+    {"__shrink__",      (PyCFunction)list_shrink, METH_NOARGS, shrink_doc},
     {"clear",           (PyCFunction)listclear,   METH_NOARGS, clear_doc},
     {"copy",            (PyCFunction)listcopy,   METH_NOARGS, copy_doc},
     {"append",          (PyCFunction)listappend,  METH_O, append_doc},
@@ -2526,7 +2569,7 @@
             }
 
             Py_SIZE(self) -= slicelength;
-            list_resize(self, Py_SIZE(self));
+            list_resize(self, Py_SIZE(self), 0);
 
             for (i = 0; i < slicelength; i++) {
                 Py_DECREF(garbage[i]);