Fixed #8285: signal handlers that aren't functions work under DEBUG. This slightly loosens the sanity check, but things that are valid under production shouldn't fail under debug.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8546 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/dispatch/dispatcher.py

@@ -63,10 +63,26 @@ class Signal(object):
         """
         from django.conf import settings
         
+        # If DEBUG is on, check that we got a good receiver
         if settings.DEBUG:
             import inspect
-            assert inspect.getargspec(receiver)[2] is not None, \
-                "Signal receivers must accept keyword arguments (**kwargs)."
+            assert callable(receiver), "Signal receivers must be callable."
+            
+            # Check for **kwargs
+            # Not all callables are inspectable with getargspec, so we'll
+            # try a couple different ways but in the end fall back on assuming
+            # it is -- we don't want to prevent registration of valid but weird
+            # callables.
+            try:
+                argspec = inspect.getargspec(receiver)
+            except TypeError:
+                try:
+                    argspec = inspect.getargspec(receiver.__call__)
+                except (TypeError, AttributeError):
+                    argspec = None
+            if argspec:
+                assert argspec[2] is not None, \
+                    "Signal receivers must accept keyword arguments (**kwargs)."
         
         if dispatch_uid:
             lookup_key = (dispatch_uid, _make_id(sender))