A WorkOrder is only as long as its PFrags.

nkms/policy/models.py

@@ -308,6 +308,9 @@ class WorkOrder(object):
     def __eq__(self, other):
         return (self.receipt_bytes, self.receipt_signature) == (other.receipt_bytes, other.receipt_signature)
 
+    def __len__(self):
+        return len(self.pfrags)
+
     @classmethod
     def constructed_by_bob(cls, kfrag_hrac, pfrags, ursula_dht_key, bob):
         receipt_bytes = b"wo:" + ursula_dht_key  # TODO: represent the pfrags as bytes and hash them as part of the receipt, ie  + keccak_digest(b"".join(pfrags))  - See #137