--- a/mercurial/util.py	Wed Oct 31 22:29:05 2018 +0900
+++ b/mercurial/util.py	Sun Nov 04 16:57:05 2018 +0900
@@ -1320,7 +1320,16 @@
         self.insert(k, v)
 
     def __delitem__(self, k):
-        node = self._cache.pop(k)
+        self.pop(k)
+
+    def pop(self, k, default=_notset):
+        try:
+            node = self._cache.pop(k)
+        except KeyError:
+            if default is _notset:
+                raise
+            return default
+        value = node.value
         self.totalcost -= node.cost
         node.markempty()
 
@@ -1329,6 +1338,8 @@
         self._movetohead(node)
         self._head = node.next
 
+        return value
+
     # Additional dict methods.
 
     def get(self, k, default=None):

--- a/tests/test-lrucachedict.py	Wed Oct 31 22:29:05 2018 +0900
+++ b/tests/test-lrucachedict.py	Sun Nov 04 16:57:05 2018 +0900
@@ -94,6 +94,21 @@
         self.assertEqual(d.peek('a'), 'va')
         self.assertEqual(list(d), ['c', 'b', 'a'])
 
+    def testpop(self):
+        d = util.lrucachedict(4)
+        d['a'] = 'va'
+        d['b'] = 'vb'
+        d['c'] = 'vc'
+
+        with self.assertRaises(KeyError):
+            d.pop('missing')
+        self.assertEqual(list(d), ['c', 'b', 'a'])
+        self.assertIsNone(d.pop('missing', None))
+        self.assertEqual(list(d), ['c', 'b', 'a'])
+
+        self.assertEqual(d.pop('b'), 'vb')
+        self.assertEqual(list(d), ['c', 'a'])
+
     def testcopypartial(self):
         d = util.lrucachedict(4)
         d.insert('a', 'va', cost=4)