[Apply SF patch #504943]

This patch makes it possible to pass Warning instances as the first
argument to warnings.warn. In this case the category argument
will be ignored. The message text used will be str(warninginstance).

Lib/warnings.py

@@ -11,6 +11,9 @@ onceregistry = {}
 
 def warn(message, category=None, stacklevel=1):
     """Issue a warning, or maybe ignore it or raise an exception."""
+    # Check if message is already a Warning object
+    if isinstance(message, Warning):
+       category = message.__class__
     # Check category argument
     if category is None:
         category = UserWarning
@@ -49,14 +52,20 @@ def warn_explicit(message, category, filename, lineno,
             module = module[:-3] # XXX What about leading pathname?
     if registry is None:
         registry = {}
-    key = (message, category, lineno)
+    if isinstance(message, Warning):
+       text = str(message)
+       category = message.__class__
+    else:
+       text = message
+       message = category(message)
+    key = (text, category, lineno)
     # Quick test for common case
     if registry.get(key):
         return
     # Search the filters
     for item in filters:
         action, msg, cat, mod, ln = item
-        if (msg.match(message) and
+        if (msg.match(text) and
             issubclass(category, cat) and
             mod.match(module) and
             (ln == 0 or lineno == ln)):
@@ -68,11 +77,11 @@ def warn_explicit(message, category, filename, lineno,
         registry[key] = 1
         return
     if action == "error":
-        raise category(message)
+        raise message
     # Other actions
     if action == "once":
         registry[key] = 1
-        oncekey = (message, category)
+        oncekey = (text, category)
         if onceregistry.get(oncekey):
             return
         onceregistry[oncekey] = 1
@@ -80,7 +89,7 @@ def warn_explicit(message, category, filename, lineno,
         pass
     elif action == "module":
         registry[key] = 1
-        altkey = (message, category, 0)
+        altkey = (text, category, 0)
         if registry.get(altkey):
             return
         registry[altkey] = 1