Settled on an extra argument to __next__() and next() to distinguish

between values and exceptions.

pep-0340.txt

@@ -287,29 +287,42 @@ Specification: Alternative __next__() and Generator Exception Handling
 
     The above specification doesn't let the generator handle general
     exceptions.  If we want that, we could modify the __next__() API
-    to take either a value or an exception argument.  When it is an
-    Exception instance, it is raised at the point of the resuming
-    yield; otherwise it is returned from the yield-expression (or
-    ignored by a yield-statement).  Wrapping a regular value in a
-    ContinueIteration is then no longer necessary.  The translation of
-    a block-statement would become:
+    to take either a value or an exception argument, with an
+    additional flag argument to distinguish between the two.  When the
+    second argument is True, the first must be an Exception instance,
+    which raised at the point of the resuming yield; otherwise the
+    first argument is the value that is returned from the
+    yield-expression (or ignored by a yield-statement).  Wrapping a
+    regular value in a ContinueIteration is then no longer necessary.
+
+    The next() built-in would be modified likewise:
+
+        def next(itr, arg=None, exc=False):
+            nxt = getattr(itr, "__next__", None)
+            if nxt is not None:
+                return nxt(arg, exc)
+            if arg is None and not exc:
+                return itr.next()
+            raise TypeError("next() with args for old-style iterator")
+
+    The translation of a block-statement would become:
 
         itr = EXPR1
         arg = val = None
-        ret = False
+        ret = exc = False
         while True:
             try:
-                VAR1 = next(itr, arg)
+                VAR1 = next(itr, arg, exc)
             except StopIteration:
                 if ret:
                     return val
                 break
             try:
                 arg = val = None
-                ret = False
+                ret = exc = False
                 BLOCK1
             except Exception, arg:
-                pass
+                exc = True
 
     The translation of "continue EXPR2" would become:
 
@@ -319,6 +332,7 @@ Specification: Alternative __next__() and Generator Exception Handling
     The translation of "break" inside a block-statement would become:
 
         arg = StopIteration()
+        exc = True
         continue
 
     The translation of "return EXPR3" inside a block-statement would
@@ -326,7 +340,7 @@ Specification: Alternative __next__() and Generator Exception Handling
 
         val = EXPR3
         arg = StopIteration()
-        ret = True
+        ret = exc = True
         continue
 
     The translation of a for-loop would be the same as indicated