[Python-checkins] python/nondist/peps pep-0340.txt,1.5,1.6

Thu Apr 28 00:41:50 CEST 2005

Update of /cvsroot/python/python/nondist/peps
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv13254
Modified Files:
	pep-0340.txt 
Log Message:
Settled on an extra argument to __next__() and next() to distinguish
between values and exceptions.
Index: pep-0340.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0340.txt,v
retrieving revision 1.5
retrieving revision 1.6
diff -u -d -r1.5 -r1.6

--- pep-0340.txt	27 Apr 2005 21:54:27 -0000	1.5
+++ pep-0340.txt	27 Apr 2005 22:41:48 -0000	1.6
@@ -287,29 +287,42 @@
 
 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 @@
 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 @@
 
 val = EXPR3
 arg = StopIteration()
- ret = True
+ ret = exc = True
 continue
 
 The translation of a for-loop would be the same as indicated
