- Fixed bug that affected many classes of event, particularly

ORM events but also engine events, where the usual logic of
"de duplicating" a redundant call to :func:`.event.listen`
with the same arguments would fail, for those events where the
listener function is wrapped.  An assertion would be hit within
registry.py.  This assertion has now been integrated into the
deduplication check, with the added bonus of a simpler means
of checking deduplication across the board.
fixes #3199

2 files changed, 17 insertions, 15 deletions

diff --git a/lib/sqlalchemy/event/attr.py b/lib/sqlalchemy/event/attr.py
index dba1063cf..be2a82208 100644
--- a/lib/sqlalchemy/event/attr.py
+++ b/lib/sqlalchemy/event/attr.py
@@ -319,14 +319,12 @@ class _ListenerCollection(RefCollection, _CompoundListener):
         registry._stored_in_collection_multi(self, other, to_associate)
 
     def insert(self, event_key, propagate):
-        if event_key._listen_fn not in self.listeners:
-            event_key.prepend_to_list(self, self.listeners)
+        if event_key.prepend_to_list(self, self.listeners):
             if propagate:
                 self.propagate.add(event_key._listen_fn)
 
     def append(self, event_key, propagate):
-        if event_key._listen_fn not in self.listeners:
-            event_key.append_to_list(self, self.listeners)
+        if event_key.append_to_list(self, self.listeners):
             if propagate:
                 self.propagate.add(event_key._listen_fn)
 
diff --git a/lib/sqlalchemy/event/registry.py b/lib/sqlalchemy/event/registry.py
index ba2f671a3..217cf7d44 100644
--- a/lib/sqlalchemy/event/registry.py
+++ b/lib/sqlalchemy/event/registry.py
@@ -71,13 +71,15 @@ def _stored_in_collection(event_key, owner):
     listen_ref = weakref.ref(event_key._listen_fn)
 
     if owner_ref in dispatch_reg:
-        assert dispatch_reg[owner_ref] == listen_ref
-    else:
-        dispatch_reg[owner_ref] = listen_ref
+        return False
+
+    dispatch_reg[owner_ref] = listen_ref
 
     listener_to_key = _collection_to_key[owner_ref]
     listener_to_key[listen_ref] = key
 
+    return True
+
 
 def _removed_from_collection(event_key, owner):
     key = event_key._key
@@ -229,18 +231,20 @@ class _EventKey(object):
     def _listen_fn(self):
         return self.fn_wrap or self.fn
 
-    def append_value_to_list(self, owner, list_, value):
-        _stored_in_collection(self, owner)
-        list_.append(value)
-
     def append_to_list(self, owner, list_):
-        _stored_in_collection(self, owner)
-        list_.append(self._listen_fn)
+        if _stored_in_collection(self, owner):
+            list_.append(self._listen_fn)
+            return True
+        else:
+            return False
 
     def remove_from_list(self, owner, list_):
         _removed_from_collection(self, owner)
         list_.remove(self._listen_fn)
 
     def prepend_to_list(self, owner, list_):
-        _stored_in_collection(self, owner)
-        list_.appendleft(self._listen_fn)
+        if _stored_in_collection(self, owner):
+            list_.appendleft(self._listen_fn)
+            return True
+        else:
+            return False