diff --git a/scapy/packet.py b/scapy/packet.py
index c1374d2a406636bac731e0f68b15fcc1b7a47206..c0cd7ac261abfae8b95879b3679eb8e91b502780 100644
--- a/scapy/packet.py
+++ b/scapy/packet.py
@@ -41,6 +41,8 @@ class Packet(BasePacket):
         # then payload and underlayer
         "payload", "underlayer",
         "name",
+        # used for sr()
+        "_answered",
     ]
     __metaclass__ = Packet_metaclass
     name = None
diff --git a/scapy/plist.py b/scapy/plist.py
index 78b6f4a5ec12ccce361f7d489e29fc35e9c0b54d..fefbfcdd391997e261d8aa5f9c99714fe5e3982a 100644
--- a/scapy/plist.py
+++ b/scapy/plist.py
@@ -40,6 +40,8 @@ class PacketList(BasePacketList):
             res = res.res
         self.res = res
         self.listname = name
+    def __len__(self):
+        return len(self.res)
     def _elt2pkt(self, elt):
         return elt
     def _elt2sum(self, elt):