1 files changed, 44 insertions, 0 deletions
diff --git a/lib/sqlalchemy/event.py b/lib/sqlalchemy/event.py
new file mode 100644
index 000000000..1b0b62b34
--- /dev/null
+++ b/lib/sqlalchemy/event.py
@@ -0,0 +1,44 @@
+from sqlalchemy import util
+
+def listen(fn, identifier, target, *args):
+    """Listen for events, passing to fn."""
+    
+    target._dispatch.append(fn, identifier, target, *args)
+
+NO_RESULT = util.symbol('no_result')
+
+
+class Dispatch(object):
+        
+    def append(self, identifier, fn, target):
+        getattr(self, identifier).append(fn)
+    
+    def __getattr__(self, key):
+        self.__dict__[key] = coll = []
+        return coll
+    
+    def chain(self, identifier, chain_kw, **kw):
+        ret = NO_RESULT
+        for fn in getattr(self, identifier):
+            ret = fn(**kw)
+            kw['chain_kw'] = ret
+        return ret
+            
+    def __call__(self, identifier, **kw):
+        for fn in getattr(self, identifier):
+            fn(**kw)
+        
+        
+class dispatcher(object):
+    def __init__(self, dispatch_cls=Dispatch):
+        self.dispatch_cls = dispatch_cls
+        self._dispatch = dispatch_cls()
+        
+    def __get__(self, obj, cls):
+        if obj is None:
+            return self._dispatch
+        obj.__dict__['_dispatch'] = disp = self.dispatch_cls()
+        for key in self._dispatch.__dict__:
+            if key.startswith('on_'):
+                disp.__dict__[key] = self._dispatch.__dict__[k].copy()
+        return disp