[Python-checkins] python/nondist/peps pep-0340.txt,1.3,1.4

[gvanrossum at users.sourceforge.net]

Update of /cvsroot/python/python/nondist/peps
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv29289

Modified Files:
	pep-0340.txt 
Log Message:
Add an alternative __next__() API to pass arbitrary exceptions in.  I
like this better.


Index: pep-0340.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0340.txt,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -d -r1.3 -r1.4
--- pep-0340.txt	27 Apr 2005 17:41:44 -0000	1.3
+++ pep-0340.txt	27 Apr 2005 21:12:49 -0000	1.4
@@ -282,6 +282,57 @@
     cases work differently; in Python, you cannot save the block for
     later use, and you cannot test whether there is a block or not.
 
+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:
+
+        itr = EXPR1
+        arg = val = None
+        ret = False
+        while True:
+            try:
+                VAR1 = next(itr, arg)
+            except StopIteration:
+                if ret:
+                    return val
+                break
+            try:
+                arg = val = None
+                ret = False
+                BLOCK1
+            except Exception, arg:
+                pass
+
+    The translation of "continue EXPR2" would become:
+
+        arg = EXPR2
+        continue
+
+    The translation of "break" inside a block-statement would become:
+
+        arg = StopIteration()
+        continue
+
+    The translation of "return EXPR3" inside a block-statement would
+    become:
+
+        val = EXPR3
+        arg = StopIteration()
+        ret = True
+        continue
+
+    The translation of a for-loop would be the same as indicated
+    earlier (inside a for-loop only the translation of "continue
+    EXPR2" is changed; break and return translate to themselves in
+    that case).
+
 Alternatives Considered
 
     TBD.