Merge pull request #14 from normanyahq/master

Add peek_first_item() and peek_last_item()

Author: amitdev

README.rst

@@ -16,11 +16,18 @@ This can be used to build a LRU cache. Usage is almost like a dict.
 
   from lru import LRU
   l = LRU(5)         # Create an LRU container that can hold 5 items
+
+  print l.peek_first_item(), l.peek_last_item()  #return the MRU key and LRU key
+  # Would print None None
+
   for i in range(5):
      l[i] = str(i)
   print l.items()    # Prints items in MRU order
   # Would print [(4, '4'), (3, '3'), (2, '2'), (1, '1'), (0, '0')]
 
+  print l.peek_first_item(), l.peek_last_item()  #return the MRU key and LRU key
+  # Would print (4, '4') (0, '0')
+
   l[5] = '5'         # Inserting one more item should evict the old item
   print l.items()
   # Would print [(5, '5'), (4, '4'), (3, '3'), (2, '2'), (1, '1')]
@@ -87,4 +94,3 @@ be similar with other python implementations as well).
   Time : 3.31 s, Memory : 453672 Kb
   $ python bench.py lru.LRU
   Time : 0.23 s, Memory : 124328 Kb
-

lru.c

@@ -167,7 +167,7 @@ static void
 lru_delete_last(LRU *self)
 {
     Node* n = self->last;
-    
+
     if (!self->last)
         return;
 
@@ -238,7 +238,7 @@ LRU_get(LRU *self, PyObject *args)
 
     if (!PyArg_ParseTuple(args, "O|O", &key, &instead))
         return NULL;
-    
+
     result = lru_subscript(self, key);
     PyErr_Clear();  /* GET_NODE sets an exception on miss. Shut it up. */
     if (result)
@@ -332,6 +332,34 @@ get_key(Node *node)
     return node->key;
 }
 
+static PyObject *
+LRU_peek_first_item(LRU *self)
+{
+    if (self->first) {
+        PyObject *tuple = PyTuple_New(2);
+        Py_INCREF(self->first->key);
+        PyTuple_SET_ITEM(tuple, 0, self->first->key);
+        Py_INCREF(self->first->value);
+        PyTuple_SET_ITEM(tuple, 1, self->first->value);
+        return tuple;
+    }
+    else Py_RETURN_NONE;
+}
+
+static PyObject *
+LRU_peek_last_item(LRU *self)
+{
+    if (self->last) {
+        PyObject *tuple = PyTuple_New(2);
+        Py_INCREF(self->last->key);
+        PyTuple_SET_ITEM(tuple, 0, self->last->key);
+        Py_INCREF(self->last->value);
+        PyTuple_SET_ITEM(tuple, 1, self->last->value);
+        return tuple;
+    }
+    else Py_RETURN_NONE;
+}
+
 static PyObject *
 LRU_keys(LRU *self) {
     return collect(self, get_key);
@@ -451,6 +479,10 @@ static PyMethodDef LRU_methods[] = {
                     PyDoc_STR("L.clear() -> clear LRU")},
     {"get_stats", (PyCFunction)LRU_get_stats, METH_NOARGS,
                     PyDoc_STR("L.get_stats() -> returns a tuple with cache hits and misses")},
+    {"peek_first_item", (PyCFunction)LRU_peek_first_item, METH_NOARGS,
+                    PyDoc_STR("L.peek_first_item() -> returns the MRU item (key,value) without changing key order")},
+    {"peek_last_item", (PyCFunction)LRU_peek_last_item, METH_NOARGS,
+                    PyDoc_STR("L.peek_last_item() -> returns the LRU item (key,value) without changing key order")},
     {NULL,	NULL},
 };
 

test/test_lru.py

@@ -106,6 +106,20 @@ def test_access(self):
                 self.assertEqual(l[i], str(i))
                 self.assertEqual(l.get(i,None), str(i))
 
+    def test_peek_first_item(self):
+        l = LRU(2)
+        self.assertEqual(None, l.peek_first_item())
+        l[1] = '1'
+        l[2] = '2'
+        self.assertEqual((2, '2'), l.peek_first_item())
+
+    def test_peek_last_item(self):
+        l = LRU(2)
+        self.assertEqual(None, l.peek_last_item())
+        l[1] = '1'
+        l[2] = '2'
+        self.assertEqual((1, '1'), l.peek_last_item())
+
     def test_overwrite(self):
         l = LRU(1)
         l[1] = '2'