# HG changeset patch
# User Nick Coghlan <ncoghlan@gmail.com>
# Date 1310224188 -36000
# Node ID 79088efb6c91fcd18825ee81f088f9c2167c5019
# Parent  3a4b983dd70b95a50ba25fc0317ac6c79481e9bc
PEP 380: support yielding from subgenerators (patch by Greg Ewing and Renauld Blanch)

diff -r 3a4b983dd70b -r 79088efb6c91 Doc/whatsnew/3.3.rst
--- a/Doc/whatsnew/3.3.rst	Sat Jul 09 11:48:50 2011 +0200
+++ b/Doc/whatsnew/3.3.rst	Sun Jul 10 01:09:48 2011 +1000
@@ -55,6 +55,21 @@
 =============
 
 
+PEP 380: Syntax for Delegating to a Subgenerator
+================================================
+
+PEP 380 adds the ``yield from`` expression, allowing a generator to delegate
+part of its operations to another generator. This allows a section of code
+containing 'yield' to be factored out and placed in another generator.
+Additionally, the subgenerator is allowed to return with a value, and the
+value is made available to the delegating generator.
+
+While designed primarily for use in delegating to a subgenerator, the ``yield
+from`` expression actually allows delegation to arbitrary subiterators.
+
+(Implementation by Greg Ewing and Renauld Blanch)
+
+
 Other Language Changes
 ======================
 
diff -r 3a4b983dd70b -r 79088efb6c91 Grammar/Grammar
--- a/Grammar/Grammar	Sat Jul 09 11:48:50 2011 +0200
+++ b/Grammar/Grammar	Sun Jul 10 01:09:48 2011 +1000
@@ -119,7 +119,7 @@
                          |'**' test)
 # The reason that keywords are test nodes instead of NAME is that using NAME
 # results in an ambiguity. ast.c makes sure it's a NAME.
-argument: test [comp_for] | test '=' test  # Really [keyword '='] test
+argument: (test | yield_from) [comp_for] | test '=' (test | yield_from)  # Really [keyword '='] test
 comp_iter: comp_for | comp_if
 comp_for: 'for' exprlist 'in' or_test [comp_iter]
 comp_if: 'if' test_nocond [comp_iter]
@@ -127,4 +127,6 @@
 # not used in grammar, but may appear in "node" passed from Parser to Compiler
 encoding_decl: NAME
 
-yield_expr: 'yield' [testlist]
+yield_expr: 'yield' [yield_arg]
+yield_arg: 'from' test | testlist
+yield_from: 'yield' 'from' test
diff -r 3a4b983dd70b -r 79088efb6c91 Include/Python-ast.h
--- a/Include/Python-ast.h	Sat Jul 09 11:48:50 2011 +0200
+++ b/Include/Python-ast.h	Sun Jul 10 01:09:48 2011 +1000
@@ -245,6 +245,7 @@
                 } GeneratorExp;
                 
                 struct {
+                        int is_from;
                         expr_ty value;
                 } Yield;
                 
@@ -487,8 +488,9 @@
 #define GeneratorExp(a0, a1, a2, a3, a4) _Py_GeneratorExp(a0, a1, a2, a3, a4)
 expr_ty _Py_GeneratorExp(expr_ty elt, asdl_seq * generators, int lineno, int
                          col_offset, PyArena *arena);
-#define Yield(a0, a1, a2, a3) _Py_Yield(a0, a1, a2, a3)
-expr_ty _Py_Yield(expr_ty value, int lineno, int col_offset, PyArena *arena);
+#define Yield(a0, a1, a2, a3, a4) _Py_Yield(a0, a1, a2, a3, a4)
+expr_ty _Py_Yield(int is_from, expr_ty value, int lineno, int col_offset,
+                  PyArena *arena);
 #define Compare(a0, a1, a2, a3, a4, a5) _Py_Compare(a0, a1, a2, a3, a4, a5)
 expr_ty _Py_Compare(expr_ty left, asdl_int_seq * ops, asdl_seq * comparators,
                     int lineno, int col_offset, PyArena *arena);
diff -r 3a4b983dd70b -r 79088efb6c91 Include/frameobject.h
--- a/Include/frameobject.h	Sat Jul 09 11:48:50 2011 +0200
+++ b/Include/frameobject.h	Sun Jul 10 01:09:48 2011 +1000
@@ -27,6 +27,7 @@
        to the current stack top. */
     PyObject **f_stacktop;
     PyObject *f_trace;		/* Trace function */
+    PyObject *f_yieldfrom;      /* Iterator being delegated to by yield from */
 
 	/* In a generator, we need to be able to swap between the exception
 	   state inside the generator and the exception state of the calling
diff -r 3a4b983dd70b -r 79088efb6c91 Include/genobject.h
--- a/Include/genobject.h	Sat Jul 09 11:48:50 2011 +0200
+++ b/Include/genobject.h	Sun Jul 10 01:09:48 2011 +1000
@@ -34,6 +34,7 @@
 
 PyAPI_FUNC(PyObject *) PyGen_New(struct _frame *);
 PyAPI_FUNC(int) PyGen_NeedsFinalizing(PyGenObject *);
+PyAPI_FUNC(int) PyGen_FetchStopIterationValue(PyObject **);
 
 #ifdef __cplusplus
 }
diff -r 3a4b983dd70b -r 79088efb6c91 Include/graminit.h
--- a/Include/graminit.h	Sat Jul 09 11:48:50 2011 +0200
+++ b/Include/graminit.h	Sun Jul 10 01:09:48 2011 +1000
@@ -81,3 +81,5 @@
 #define comp_if 334
 #define encoding_decl 335
 #define yield_expr 336
+#define yield_arg 337
+#define yield_from 338
diff -r 3a4b983dd70b -r 79088efb6c91 Include/opcode.h
--- a/Include/opcode.h	Sat Jul 09 11:48:50 2011 +0200
+++ b/Include/opcode.h	Sun Jul 10 01:09:48 2011 +1000
@@ -53,6 +53,7 @@
 #define STORE_LOCALS	69
 #define PRINT_EXPR	70
 #define LOAD_BUILD_CLASS 71
+#define YIELD_FROM	72
 
 #define INPLACE_LSHIFT	75
 #define INPLACE_RSHIFT	76
diff -r 3a4b983dd70b -r 79088efb6c91 Include/pyerrors.h
--- a/Include/pyerrors.h	Sat Jul 09 11:48:50 2011 +0200
+++ b/Include/pyerrors.h	Sun Jul 10 01:09:48 2011 +1000
@@ -47,6 +47,11 @@
     PyObject *filename;
 } PyEnvironmentErrorObject;
 
+typedef struct {
+    PyException_HEAD
+    PyObject *value;
+} PyStopIterationObject;
+
 #ifdef MS_WINDOWS
 typedef struct {
     PyException_HEAD
@@ -356,6 +361,8 @@
     const char *reason          /* UTF-8 encoded string */
     );
 
+/* create a StopIteration exception with the given value */
+PyAPI_FUNC(PyObject *) PyStopIteration_New(PyObject *);
 
 /* These APIs aren't really part of the error implementation, but
    often needed to format error messages; the native C lib APIs are
diff -r 3a4b983dd70b -r 79088efb6c91 Lib/opcode.py
--- a/Lib/opcode.py	Sat Jul 09 11:48:50 2011 +0200
+++ b/Lib/opcode.py	Sun Jul 10 01:09:48 2011 +1000
@@ -88,6 +88,7 @@
 
 def_op('PRINT_EXPR', 70)
 def_op('LOAD_BUILD_CLASS', 71)
+def_op('YIELD_FROM', 72)
 
 def_op('INPLACE_LSHIFT', 75)
 def_op('INPLACE_RSHIFT', 76)
diff -r 3a4b983dd70b -r 79088efb6c91 Lib/test/test_generators.py
--- a/Lib/test/test_generators.py	Sat Jul 09 11:48:50 2011 +0200
+++ b/Lib/test/test_generators.py	Sun Jul 10 01:09:48 2011 +1000
@@ -728,29 +728,6 @@
 
 syntax_tests = """
 
->>> def f():
-...     return 22
-...     yield 1
-Traceback (most recent call last):
-  ..
-SyntaxError: 'return' with argument inside generator
-
->>> def f():
-...     yield 1
-...     return 22
-Traceback (most recent call last):
-  ..
-SyntaxError: 'return' with argument inside generator
-
-"return None" is not the same as "return" in a generator:
-
->>> def f():
-...     yield 1
-...     return None
-Traceback (most recent call last):
-  ..
-SyntaxError: 'return' with argument inside generator
-
 These are fine:
 
 >>> def f():
@@ -866,20 +843,6 @@
 >>> type(f())
 <class 'generator'>
 
-
->>> def f():
-...     if 0:
-...         lambda x:  x        # shouldn't trigger here
-...         return              # or here
-...         def f(i):
-...             return 2*i      # or here
-...         if 0:
-...             return 3        # but *this* sucks (line 8)
-...     if 0:
-...         yield 2             # because it's a generator (line 10)
-Traceback (most recent call last):
-SyntaxError: 'return' with argument inside generator
-
 This one caused a crash (see SF bug 567538):
 
 >>> def f():
@@ -1566,11 +1529,6 @@
   ...
 SyntaxError: 'yield' outside function
 
->>> def f(): return lambda x=(yield): 1
-Traceback (most recent call last):
-  ...
-SyntaxError: 'return' with argument inside generator
-
 >>> def f(): x = yield = y
 Traceback (most recent call last):
   ...
diff -r 3a4b983dd70b -r 79088efb6c91 Lib/test/test_grammar.py
--- a/Lib/test/test_grammar.py	Sat Jul 09 11:48:50 2011 +0200
+++ b/Lib/test/test_grammar.py	Sun Jul 10 01:09:48 2011 +1000
@@ -459,6 +459,7 @@
 
     def test_yield(self):
         check_syntax_error(self, "class foo:yield 1")
+        check_syntax_error(self, "yield from")
 
     def test_raise(self):
         # 'raise' test [',' test]
diff -r 3a4b983dd70b -r 79088efb6c91 Lib/test/test_parser.py
--- a/Lib/test/test_parser.py	Sat Jul 09 11:48:50 2011 +0200
+++ b/Lib/test/test_parser.py	Sun Jul 10 01:09:48 2011 +1000
@@ -50,6 +50,10 @@
         self.check_suite("def f(): (yield 1)*2")
         self.check_suite("def f(): return; yield 1")
         self.check_suite("def f(): yield 1; return")
+        self.check_suite("def f(): yield from 1")
+        self.check_suite("def f(): x = yield from 1")
+        self.check_suite("def f(): f(yield from 1)")
+        self.check_suite("def f(): yield 1; return 1")
         self.check_suite("def f():\n"
                          "    for x in range(30):\n"
                          "        yield x\n")
diff -r 3a4b983dd70b -r 79088efb6c91 Lib/test/test_pep380.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/test/test_pep380.py	Sun Jul 10 01:09:48 2011 +1000
@@ -0,0 +1,1096 @@
+# -*- coding: utf-8 -*-
+
+"""
+Test suite for PEP 380 implementation
+
+adapted from original tests written by Greg Ewing
+see <http://www.cosc.canterbury.ac.nz/greg.ewing/python/yield-from/YieldFrom-Python3.1.2-rev5.zip>
+"""
+
+import unittest
+import io
+import sys
+import traceback
+
+# XXX (ncoghlan): The line numbers make many of these tests quite fragile.
+# Ideally the whole lot should be modified to use independent asserts rather
+# than golden output comparisons
+
+class PEP380Test(unittest.TestCase):
+    maxDiff = None
+    def setUp(self):
+        self.out = io.StringIO()
+        self.saved_stdout = sys.stdout
+        self.saved_stderr = sys.stderr
+        sys.stdout = sys.stderr = self.out
+
+    def test(self):
+        try:
+            self.case()
+        except:
+            et, ev, tb = sys.exc_info()
+            tb = tb.tb_next
+            traceback.print_exception(et, ev, tb)
+        # Trailing whitespace does not play nicely with checkin hooks
+        self.assertEqual('\n'.join(line.rstrip() for line in self.out.getvalue().split('\n')),
+                         '\n'.join(line.rstrip() for line in self.expected.split('\n')))
+
+    def tearDown(self):
+        sys.stdout = self.saved_stdout
+        sys.stderr = self.saved_stderr
+        self.out.close()
+
+
+class Test1(PEP380Test):
+    """
+    Test grammar and code generation
+    """
+
+    expected = """\
+---------- g1 ----------
+ 78           0 LOAD_CONST               0 (None)
+              3 YIELD_VALUE
+              4 POP_TOP
+
+ 79           5 LOAD_CONST               1 (42)
+              8 YIELD_VALUE
+              9 POP_TOP
+             10 LOAD_CONST               0 (None)
+             13 RETURN_VALUE
+---------- g2 ----------
+ 82           0 LOAD_GLOBAL              0 (x)
+              3 YIELD_FROM
+              4 POP_TOP
+              5 LOAD_CONST               0 (None)
+              8 RETURN_VALUE
+---------- g3 ----------
+ 85           0 LOAD_FAST                0 (x)
+              3 YIELD_FROM
+              4 STORE_FAST               0 (x)
+              7 LOAD_CONST               0 (None)
+             10 RETURN_VALUE
+""".format(__file__)
+
+    def case(self):
+        import dis
+
+        def g1():
+            yield
+            yield 42
+
+        def g2():
+            yield from x
+
+        def g3():
+            x = yield from x
+
+        def disgen(g):
+            print("---------- %s ----------" % g.__name__)
+            dis.dis(g)
+
+        disgen(g1)
+        disgen(g2)
+        disgen(g3)
+
+
+class Test2(PEP380Test):
+    """
+    Test delegation of initial next() call to subgenerator
+    """
+
+    expected = """\
+Starting g1
+Starting g2
+Yielded 42
+Finishing g2
+Finishing g1
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            print("Starting g1")
+            yield from g2()
+            print("Finishing g1")
+
+        def g2():
+            print("Starting g2")
+            yield 42
+            print("Finishing g2")
+
+        for x in g1():
+            print("Yielded", x)
+
+
+class Test3(PEP380Test):
+    """
+    Test raising exception in initial next() call
+    """
+
+    expected = """\
+Starting g1
+Starting g2
+Finishing g2
+Finishing g1
+Traceback (most recent call last):
+  File "{0}", line 159, in case
+    for x in g1():
+  File "{0}", line 148, in g1
+    yield from g2()
+  File "{0}", line 155, in g2
+    raise ValueError("spanish inquisition occurred")
+ValueError: spanish inquisition occurred
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            try:
+                print("Starting g1")
+                yield from g2()
+            finally:
+                print("Finishing g1")
+
+        def g2():
+            try:
+                print("Starting g2")
+                raise ValueError("spanish inquisition occurred")
+            finally:
+                print("Finishing g2")
+
+        for x in g1():
+            print("Yielded", x)
+
+
+class Test4(PEP380Test):
+    """
+    Test delegation of next() call to subgenerator
+    """
+
+    expected = """\
+Starting g1
+Yielded g1 ham
+Starting g2
+Yielded g2 spam
+Yielded g2 more spam
+Finishing g2
+Yielded g1 eggs
+Finishing g1
+""".format(__file__)
+
+    def case(self):
+
+        def g1():
+            print("Starting g1")
+            yield "g1 ham"
+            yield from g2()
+            yield "g1 eggs"
+            print("Finishing g1")
+
+        def g2():
+            print("Starting g2")
+            yield "g2 spam"
+            yield "g2 more spam"
+            print("Finishing g2")
+
+        for x in g1():
+            print("Yielded", x)
+
+
+class Test5(PEP380Test):
+    """
+    Test raising exception in delegated next() call
+    """
+
+    expected = """\
+Starting g1
+Yielded g1 ham
+Starting g2
+Yielded g2 spam
+Finishing g2
+Finishing g1
+Traceback (most recent call last):
+  File "{0}", line 239, in case
+    for x in g1():
+  File "{0}", line 225, in g1
+    yield from g2()
+  File "{0}", line 234, in g2
+    raise ValueError("hovercraft is full of eels")
+ValueError: hovercraft is full of eels
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            try:
+                print("Starting g1")
+                yield "g1 ham"
+                yield from g2()
+                yield "g1 eggs"
+            finally:
+                print("Finishing g1")
+
+        def g2():
+            try:
+                print("Starting g2")
+                yield "g2 spam"
+                raise ValueError("hovercraft is full of eels")
+                yield "g2 more spam"
+            finally:
+                print("Finishing g2")
+
+        for x in g1():
+            print("Yielded", x)
+
+
+class Test6(PEP380Test):
+    """
+    Test delegation of send()
+    """
+
+    expected = """\
+Starting g1
+g1 received 1
+Starting g2
+Yielded g2 spam
+g2 received 2
+Yielded g2 more spam
+g2 received 3
+Finishing g2
+Yielded g1 eggs
+g1 received 4
+Finishing g1
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            print("Starting g1")
+            x = yield "g1 ham"
+            print("g1 received", x)
+            yield from g2()
+            x = yield "g1 eggs"
+            print("g1 received", x)
+            print("Finishing g1")
+
+        def g2():
+            print("Starting g2")
+            x = yield "g2 spam"
+            print("g2 received", x)
+            x = yield "g2 more spam"
+            print("g2 received", x)
+            print("Finishing g2")
+
+        g = g1()
+        y = next(g)
+        x = 1
+        try:
+            while 1:
+                y = g.send(x)
+                print("Yielded", y)
+                x += 1
+        except StopIteration:
+            pass
+
+
+class Test7(PEP380Test):
+    """
+    Test handling exception while delegating 'send'
+    """
+
+    expected = """\
+Starting g1
+g1 received 1
+Starting g2
+Yielded g2 spam
+g2 received 2
+Traceback (most recent call last):
+  File "{0}", line 337, in case
+    y = g.send(x)
+  File "{0}", line 318, in g1
+    yield from g2()
+  File "{0}", line 327, in g2
+    raise ValueError("hovercraft is full of eels")
+ValueError: hovercraft is full of eels
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            print("Starting g1")
+            x = yield "g1 ham"
+            print("g1 received", x)
+            yield from g2()
+            x = yield "g1 eggs"
+            print("g1 received", x)
+            print("Finishing g1")
+
+        def g2():
+            print("Starting g2")
+            x = yield "g2 spam"
+            print("g2 received", x)
+            raise ValueError("hovercraft is full of eels")
+            x = yield "g2 more spam"
+            print("g2 received", x)
+            print("Finishing g2")
+
+        g = g1()
+        y = next(g)
+        x = 1
+        try:
+            while 1:
+                y = g.send(x)
+                print("Yielded", y)
+                x += 1
+        except StopIteration:
+            print("StopIteration")
+
+
+
+class Test8(PEP380Test):
+    """
+    Test delegating 'close'
+    """
+
+    expected = """\
+Starting g1
+Yielded g1 ham
+Starting g2
+Yielded g2 spam
+Finishing g2
+Finishing g1
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            try:
+                print("Starting g1")
+                yield "g1 ham"
+                yield from g2()
+                yield "g1 eggs"
+            finally:
+                print("Finishing g1")
+
+        def g2():
+            try:
+                print("Starting g2")
+                yield "g2 spam"
+                yield "g2 more spam"
+            finally:
+                print("Finishing g2")
+
+        g = g1()
+        for i in range(2):
+            x = next(g)
+            print("Yielded", x)
+        g.close()
+
+
+class Test9(PEP380Test):
+    """
+    Test handling exception while delegating 'close'
+    """
+
+    expected = """\
+Starting g1
+Yielded g1 ham
+Starting g2
+Yielded g2 spam
+Finishing g2
+Finishing g1
+Traceback (most recent call last):
+  File "{0}", line 426, in g2
+    yield "g2 spam"
+GeneratorExit
+
+During handling of the above exception, another exception occurred:
+
+Traceback (most recent call last):
+  File "{0}", line 436, in case
+    g.close()
+  File "{0}", line 418, in g1
+    yield from g2()
+  File "{0}", line 430, in g2
+    raise ValueError("nybbles have exploded with delight")
+ValueError: nybbles have exploded with delight
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            try:
+                print("Starting g1")
+                yield "g1 ham"
+                yield from g2()
+                yield "g1 eggs"
+            finally:
+                print("Finishing g1")
+
+        def g2():
+            try:
+                print("Starting g2")
+                yield "g2 spam"
+                yield "g2 more spam"
+            finally:
+                print("Finishing g2")
+                raise ValueError("nybbles have exploded with delight")
+
+        g = g1()
+        for i in range(2):
+            x = next(g)
+            print("Yielded", x)
+        g.close()
+
+
+class Test10(PEP380Test):
+    """
+    Test delegating 'throw'
+    """
+
+    expected = """\
+Starting g1
+Yielded g1 ham
+Starting g2
+Yielded g2 spam
+Finishing g2
+Finishing g1
+Traceback (most recent call last):
+  File "{0}", line 484, in case
+    g.throw(e)
+  File "{0}", line 466, in g1
+    yield from g2()
+  File "{0}", line 474, in g2
+    yield "g2 spam"
+ValueError: tomato ejected
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            try:
+                print("Starting g1")
+                yield "g1 ham"
+                yield from g2()
+                yield "g1 eggs"
+            finally:
+                print("Finishing g1")
+
+        def g2():
+            try:
+                print("Starting g2")
+                yield "g2 spam"
+                yield "g2 more spam"
+            finally:
+                print("Finishing g2")
+
+        g = g1()
+        for i in range(2):
+            x = next(g)
+            print("Yielded", x)
+        e = ValueError("tomato ejected")
+        g.throw(e)
+
+
+class Test11(PEP380Test):
+    """
+    Test 'value' attribute of StopIteration exception
+    """
+
+    expected = """\
+StopIteration:
+value = None
+StopIteration: spam
+value = spam
+StopIteration: spam
+value = eggs
+""".format(__file__)
+
+    def case(self):
+        def pex(e):
+            print("%s: %s" % (e.__class__.__name__, e))
+            print("value =", e.value)
+
+        e = StopIteration()
+        pex(e)
+        e = StopIteration("spam")
+        pex(e)
+        e.value = "eggs"
+        pex(e)
+
+
+class Test12(PEP380Test):
+    """
+    Test generator return value
+    """
+
+    expected = """\
+Starting g1
+Yielded g1 ham
+Starting g2
+Yielded g2 spam
+Yielded g2 more spam
+Finishing g2
+g2 returned None
+Starting g2
+Yielded g2 spam
+Yielded g2 more spam
+Finishing g2
+g2 returned 42
+Yielded g1 eggs
+Finishing g1
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            print("Starting g1")
+            yield "g1 ham"
+            ret = yield from g2()
+            print("g2 returned", ret)
+            ret = yield from g2(42)
+            print("g2 returned", ret)
+            yield "g1 eggs"
+            print("Finishing g1")
+
+        def g2(v = None):
+            print("Starting g2")
+            yield "g2 spam"
+            yield "g2 more spam"
+            print("Finishing g2")
+            if v:
+                return v
+
+        for x in g1():
+            print("Yielded", x)
+
+
+class Test13(PEP380Test):
+    """
+    Test delegation of next() to non-generator
+    """
+
+    expected = """\
+Yielded 0
+Yielded 1
+Yielded 2
+""".format(__file__)
+
+    def case(self):
+        def g():
+            yield from range(3)
+
+        for x in g():
+            print("Yielded", x)
+
+
+class Test14(PEP380Test):
+    """
+    Test conversion of send(None) to next()
+    """
+
+    expected = """\
+Yielded: 0
+Yielded: 1
+Yielded: 2
+""".format(__file__)
+
+    def case(self):
+        def g():
+            yield from range(3)
+
+        gi = g()
+        for x in range(3):
+            y = gi.send(None)
+            print("Yielded:", y)
+
+
+class Test15(PEP380Test):
+    """
+    Test delegation of close() to non-generator
+    """
+
+    expected = """\
+starting g
+finishing g
+""".format(__file__)
+
+    def case(self):
+        def g():
+            try:
+                print("starting g")
+                yield from range(3)
+                print("g should not be here")
+            finally:
+                print("finishing g")
+
+        gi = g()
+        next(gi)
+        gi.close()
+
+
+class Test16(PEP380Test):
+    """
+    Test delegating 'throw' to non-generator
+    """
+
+    expected = """\
+Starting g
+Yielded 0
+Yielded 1
+Yielded 2
+Yielded 3
+Yielded 4
+Finishing g
+Traceback (most recent call last):
+  File "{0}", line 657, in case
+    gi.throw(e)
+  File "{0}", line 648, in g
+    yield from range(10)
+ValueError: tomato ejected
+""".format(__file__)
+
+    def case(self):
+        def g():
+            try:
+                print("Starting g")
+                yield from range(10)
+            finally:
+                print("Finishing g")
+
+        gi = g()
+        for i in range(5):
+            x = next(gi)
+            print("Yielded", x)
+        e = ValueError("tomato ejected")
+        gi.throw(e)
+
+
+class Test17(PEP380Test):
+    """
+    Test attempting to send to non-generator
+    """
+
+    expected = """\
+starting g
+finishing g
+Traceback (most recent call last):
+  File "{0}", line 688, in case
+    y = gi.send(42)
+  File "{0}", line 680, in g
+    yield from range(3)
+AttributeError: send
+""".format(__file__)
+
+    def case(self):
+        def g():
+            try:
+                print("starting g")
+                yield from range(3)
+                print("g should not be here")
+            finally:
+                print("finishing g")
+
+        gi = g()
+        next(gi)
+        for x in range(3):
+            y = gi.send(42)
+            print("Should not have yielded:", y)
+
+
+class Test18(PEP380Test):
+    """
+    Test exception in initial next() call
+    """
+
+    expected = """\
+g1 about to yield from g2
+Traceback (most recent call last):
+  File "{0}", line 719, in case
+    next(gi)
+  File "{0}", line 712, in g1
+    yield from g2()
+  File "{0}", line 716, in g2
+    yield 1/0
+ZeroDivisionError: division by zero
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            print("g1 about to yield from g2")
+            yield from g2()
+            print("g1 should not be here")
+
+        def g2():
+            yield 1/0
+
+        gi = g1()
+        next(gi)
+
+
+class Test19(PEP380Test):
+    """
+    Test attempted yield-from loop
+    """
+
+    expected = """\
+g1: starting
+Yielded: y1
+g1: about to yield from g2
+g2: starting
+Yielded: y2
+g2: about to yield from g1
+Traceback (most recent call last):
+  File "{0}", line 760, in case
+    for y in gi:
+  File "{0}", line 756, in g2
+    yield from gi
+  File "{0}", line 749, in g1
+    yield from g2()
+ValueError: generator already executing
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            print("g1: starting")
+            yield "y1"
+            print("g1: about to yield from g2")
+            yield from g2()
+            print("g1 should not be here")
+
+        def g2():
+            print("g2: starting")
+            yield "y2"
+            print("g2: about to yield from g1")
+            yield from gi
+            print("g2 should not be here")
+
+        gi = g1()
+        for y in gi:
+            print("Yielded:", y)
+
+
+class Test20(PEP380Test):
+    """
+    Test returning value from delegated 'throw'
+    """
+
+    expected = """\
+Starting g1
+Yielded g1 ham
+Starting g2
+Yielded g2 spam
+Caught LunchError in g2
+Yielded g2 yet more spam
+Yielded g1 eggs
+Finishing g1
+""".format(__file__)
+
+    def case(self):
+        def g1():
+            try:
+                print("Starting g1")
+                yield "g1 ham"
+                yield from g2()
+                yield "g1 eggs"
+            finally:
+                print("Finishing g1")
+
+        def g2():
+            try:
+                print("Starting g2")
+                yield "g2 spam"
+                yield "g2 more spam"
+            except LunchError:
+                print("Caught LunchError in g2")
+                yield "g2 lunch saved"
+                yield "g2 yet more spam"
+
+        class LunchError(Exception):
+            pass
+
+        g = g1()
+        for i in range(2):
+            x = next(g)
+            print("Yielded", x)
+        e = LunchError("tomato ejected")
+        g.throw(e)
+        for x in g:
+            print("Yielded", x)
+
+
+class Test21(PEP380Test):
+    """
+    Test next and return with value
+    """
+
+    expected = """\
+g starting
+f resuming g
+g returning None
+f caught StopIteration()
+g starting
+f resuming g
+g returning 42
+f caught StopIteration(42,)
+""".format(__file__)
+
+    def case(self):
+        def f(r):
+            gi = g(r)
+            next(gi)
+            try:
+                print("f resuming g")
+                next(gi)
+                print("f SHOULD NOT BE HERE")
+            except StopIteration as e:
+                print("f caught", repr(e))
+
+        def g(r):
+            print("g starting")
+            yield
+            print("g returning", r)
+            return r
+
+        f(None)
+        f(42)
+
+
+class Test22(PEP380Test):
+    """
+    Test send and return with value
+    """
+
+    expected = """\
+g starting
+f sending spam to g
+g received spam
+g returning None
+f caught StopIteration()
+g starting
+f sending spam to g
+g received spam
+g returning 42
+f caught StopIteration(42,)
+""".format(__file__)
+
+    def case(self):
+        def f(r):
+            gi = g(r)
+            next(gi)
+            try:
+                print("f sending spam to g")
+                gi.send("spam")
+                print("f SHOULD NOT BE HERE")
+            except StopIteration as e:
+                print("f caught", repr(e))
+
+        def g(r):
+            print("g starting")
+            x = yield
+            print("g received", x)
+            print("g returning", r)
+            return r
+
+        f(None)
+        f(42)
+
+
+class Test23(PEP380Test):
+    """
+    Test parsing yield from as function argument
+    """
+
+    expected = """\
+909           0 LOAD_GLOBAL              0 (f)
+              3 LOAD_GLOBAL              1 (x)
+              6 YIELD_FROM
+              7 CALL_FUNCTION            1
+             10 POP_TOP
+             11 LOAD_CONST               0 (None)
+             14 RETURN_VALUE
+""".format(__file__)
+
+    def case(self):
+        from dis import dis
+
+        def g():
+            f(yield from x)
+
+        dis(g)
+
+
+class Test24(PEP380Test):
+    """
+    Test parser module
+    """
+
+    expected = """\
+(257, (268, (269, (270, (276, (280, (336, (1, 'yield'), (337, (1, 'from'), (302, (306, (307, (308, (309, (312, (313, (314, (315, (316, (317, (318, (319, (320, (2, '1')))))))))))))))))))), (4, ''))), (4, ''), (0, ''))
+True
+(257, (268, (269, (270, (271, (272, (302, (306, (307, (308, (309, (312, (313, (314, (315, (316, (317, (318, (319, (320, (1, 'f')), (322, (7, '('), (330, (331, (338, (1, 'yield'), (1, 'from'), (302, (306, (307, (308, (309, (312, (313, (314, (315, (316, (317, (318, (319, (320, (2, '1')))))))))))))))))), (8, ')')))))))))))))))))), (4, ''))), (4, ''), (0, ''))
+True
+""".format(__file__)
+
+    def case(self):
+        import parser
+
+        def test(src):
+            st1 = parser.suite(src)
+            tup1 = st1.totuple()
+            print(tup1)
+            st2 = parser.sequence2st(tup1)
+            tup2 = st2.totuple()
+            print(tup1 == tup2)
+
+        test("yield from 1")
+        test("f(yield from 1)")
+
+
+class Test25(PEP380Test):
+    """
+    Test catching an exception thrown into a
+    subgenerator and returning a value
+    """
+
+    expected = """\
+1
+inner caught ValueError
+inner returned 2 to outer
+2
+""".format(__file__)
+
+    def case(self):
+        def inner():
+            try:
+                yield 1
+            except ValueError:
+                print("inner caught ValueError") #pass
+            return 2
+
+        def outer():
+            v = yield from inner()
+            print("inner returned %r to outer" % v)
+            yield v
+
+        g = outer()
+        print(next(g))              # prints 1
+        print(g.throw(ValueError))  # prints 2
+
+
+class Test26(PEP380Test):
+    """
+    Test throwing GeneratorExit into a subgenerator that
+    catches it and returns normally.
+    """
+
+    expected = """\
+Enter g
+Enter f
+Traceback (most recent call last):
+  File "{0}", line 1005, in case
+    gi.throw(GeneratorExit)
+  File "{0}", line 1000, in g
+    yield from f()
+GeneratorExit
+""".format(__file__)
+
+    def case(self):
+        def f():
+            try:
+                print("Enter f")
+                yield
+                print("Exit f")
+            except GeneratorExit:
+                return
+
+        def g():
+            print("Enter g")
+            yield from f()
+            print("Exit g")
+
+        gi = g()
+        next(gi)
+        gi.throw(GeneratorExit)
+
+
+class Test27(PEP380Test):
+    """
+    Test throwing GeneratorExit into a subgenerator that
+    catches it and yields.
+    """
+
+    expected = """\
+Enter g
+Enter f
+Traceback (most recent call last):
+  File "{0}", line 1041, in case
+    gi.throw(GeneratorExit)
+  File "{0}", line 1036, in g
+    yield from f()
+RuntimeError: generator ignored GeneratorExit
+""".format(__file__)
+
+    def case(self):
+        def f():
+            try:
+                print("Enter f")
+                yield
+                print("Exit f")
+            except GeneratorExit:
+                yield
+
+        def g():
+            print("Enter g")
+            yield from f()
+            print("Exit g")
+
+        gi = g()
+        next(gi)
+        gi.throw(GeneratorExit)
+
+
+class Test28(PEP380Test):
+    """
+    Test throwing GeneratorExit into a subgenerator that
+    catches it and raises a different exception.
+    """
+
+    expected = """\
+Enter g
+Enter f
+Traceback (most recent call last):
+  File "{0}", line 1074, in f
+    yield
+GeneratorExit
+
+During handling of the above exception, another exception occurred:
+
+Traceback (most recent call last):
+  File "{0}", line 1086, in case
+    gi.throw(GeneratorExit)
+  File "{0}", line 1081, in g
+    yield from f()
+  File "{0}", line 1077, in f
+    raise ValueError("Vorpal bunny encountered")
+ValueError: Vorpal bunny encountered
+""".format(__file__)
+
+    def case(self):
+        def f():
+            try:
+                print("Enter f")
+                yield
+                print("Exit f")
+            except GeneratorExit:
+                raise ValueError("Vorpal bunny encountered")
+
+        def g():
+            print("Enter g")
+            yield from f()
+            print("Exit g")
+
+        gi = g()
+        next(gi)
+        gi.throw(GeneratorExit)
+
+
+def test_main():
+    from test import support
+    test_classes = [Test1, Test2, Test3, Test4, Test5, Test6, Test7, Test8, Test9, Test10, Test11, Test12, Test13, Test14, Test15, Test16, Test17, Test18, Test19, Test20, Test21, Test22, Test23, Test24, Test25, Test26, Test27, Test28]
+    support.run_unittest(*test_classes)
+
+
+if __name__ == '__main__':
+    test_main()
diff -r 3a4b983dd70b -r 79088efb6c91 Lib/test/test_sys.py
--- a/Lib/test/test_sys.py	Sat Jul 09 11:48:50 2011 +0200
+++ b/Lib/test/test_sys.py	Sun Jul 10 01:09:48 2011 +1000
@@ -726,7 +726,7 @@
         nfrees = len(x.f_code.co_freevars)
         extras = x.f_code.co_stacksize + x.f_code.co_nlocals +\
                   ncells + nfrees - 1
-        check(x, size(vh + '12P3i' + CO_MAXBLOCKS*'3i' + 'P' + extras*'P'))
+        check(x, size(vh + '13P3i' + CO_MAXBLOCKS*'3i' + 'P' + extras*'P'))
         # function
         def func(): pass
         check(func, size(h + '11P'))
diff -r 3a4b983dd70b -r 79088efb6c91 Misc/ACKS
--- a/Misc/ACKS	Sat Jul 09 11:48:50 2011 +0200
+++ b/Misc/ACKS	Sun Jul 10 01:09:48 2011 +1000
@@ -93,6 +93,7 @@
 Philippe Biondi
 Stuart Bishop
 Roy Bixler
+Renaud Blanch
 Mike Bland
 Martin Bless
 Pablo Bleyer
diff -r 3a4b983dd70b -r 79088efb6c91 Misc/NEWS
--- a/Misc/NEWS	Sat Jul 09 11:48:50 2011 +0200
+++ b/Misc/NEWS	Sun Jul 10 01:09:48 2011 +1000
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- PEP 380, Issue #11682: Add "yield from <x>" to support easy delegation to
+  subgenerators (patch by Greg Ewing and Renaud Blanch)
+
 - Issue #9611, #9015: FileIO.read() clamps the length to INT_MAX on Windows.
 
 - Issue #9642: Uniformize the tests on the availability of the mbcs codec, add
diff -r 3a4b983dd70b -r 79088efb6c91 Modules/parsermodule.c
--- a/Modules/parsermodule.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Modules/parsermodule.c	Sun Jul 10 01:09:48 2011 +1000
@@ -976,6 +976,7 @@
 VALIDATER(testlist_comp);       VALIDATER(yield_expr);
 VALIDATER(or_test);
 VALIDATER(test_nocond);         VALIDATER(lambdef_nocond);
+VALIDATER(yield_arg);           VALIDATER(yield_from);
 
 #undef VALIDATER
 
@@ -1636,22 +1637,61 @@
 }
 
 
-/* yield_expr: 'yield' [testlist]
+/* yield_expr: 'yield' [yield_arg]
  */
 static int
 validate_yield_expr(node *tree)
 {
     int nch = NCH(tree);
-    int res = (validate_ntype(tree, yield_expr)
-               && ((nch == 1) || (nch == 2))
-               && validate_name(CHILD(tree, 0), "yield"));
-
-    if (res && (nch == 2))
-        res = validate_testlist(CHILD(tree, 1));
-
-    return (res);
+    if (nch < 1 || nch > 2)
+        return 0;
+    if (!validate_ntype(tree, yield_expr))
+        return 0;
+    if (!validate_name(CHILD(tree, 0), "yield"))
+        return 0;
+    if (nch == 2) {
+        if (!validate_yield_arg(CHILD(tree, 1)))
+            return 0;
+    }
+    return 1;
 }
 
+/* yield_arg: 'from' test | testlist
+ */
+static int
+validate_yield_arg(node *tree)
+{
+    int nch = NCH(tree);
+    if (!validate_ntype(tree, yield_arg))
+        return 0;
+    if (nch == 1) {
+        if (!validate_testlist(CHILD(tree, nch - 1)))
+            return 0;
+     }
+     else if (nch == 2) {
+        if (!validate_name(CHILD(tree, 0), "from"))
+            return 0;
+        if (!validate_test(CHILD(tree, 1)))
+            return 0;
+    }
+    else
+        return 0;
+    return 1;
+}
+
+/* yield_from: 'yield' 'from' test
+ */
+static int
+validate_yield_from(node *tree)
+{
+    int nch = NCH(tree);
+    int res = (validate_ntype(tree, yield_from)
+               && (nch == 3)
+               && validate_name(CHILD(tree, 0), "yield")
+               && validate_name(CHILD(tree, 1), "from")
+               && validate_test(CHILD(tree, 2)));
+    return res;
+}
 
 /* yield_stmt: yield_expr
  */
@@ -2665,9 +2705,13 @@
 {
     int nch = NCH(tree);
     int res = (validate_ntype(tree, argument)
-               && ((nch == 1) || (nch == 2) || (nch == 3))
-               && validate_test(CHILD(tree, 0)));
-
+               && ((nch == 1) || (nch == 2) || (nch == 3)));
+    if (res) {
+        if (TYPE(CHILD(tree, 0)) == yield_from)
+            res = (nch == 1) && validate_yield_from(CHILD(tree, 0));
+        else
+            res = validate_test(CHILD(tree, 0));
+    }
     if (res && (nch == 2))
         res = validate_comp_for(CHILD(tree, 1));
     else if (res && (nch == 3))
diff -r 3a4b983dd70b -r 79088efb6c91 Objects/exceptions.c
--- a/Objects/exceptions.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Objects/exceptions.c	Sun Jul 10 01:09:48 2011 +1000
@@ -471,8 +471,65 @@
 /*
  *    StopIteration extends Exception
  */
-SimpleExtendsException(PyExc_Exception, StopIteration,
-                       "Signal the end from iterator.__next__().");
+
+//SimpleExtendsException(PyExc_Exception, StopIteration,
+//                       "Signal the end from iterator.__next__().");
+
+static PyMemberDef StopIteration_members[] = {
+    {"value", T_OBJECT, offsetof(PyStopIterationObject, value), 0,
+        PyDoc_STR("generator return value")},
+    {NULL}  /* Sentinel */
+};
+
+static int
+StopIteration_init(PyStopIterationObject *self, PyObject *args, PyObject *kwds)
+{
+    Py_ssize_t size = PyTuple_GET_SIZE(args);
+    PyObject *value;
+
+    if (BaseException_init((PyBaseExceptionObject *)self, args, kwds) == -1)
+        return -1;
+    Py_CLEAR(self->value);
+    if (size > 0)
+        value = PyTuple_GET_ITEM(args, 0);
+    else
+        value = Py_None;
+    Py_INCREF(value);
+    self->value = value;
+    return 0;
+}
+
+static int
+StopIteration_clear(PyStopIterationObject *self)
+{
+    Py_CLEAR(self->value);
+    return BaseException_clear((PyBaseExceptionObject *)self);
+}
+
+static void
+StopIteration_dealloc(PyStopIterationObject *self)
+{
+    _PyObject_GC_UNTRACK(self);
+    StopIteration_clear(self);
+    Py_TYPE(self)->tp_free((PyObject *)self);
+}
+
+static int
+StopIteration_traverse(PyStopIterationObject *self, visitproc visit, void *arg)
+{
+    Py_VISIT(self->value);
+    return BaseException_traverse((PyBaseExceptionObject *)self, visit, arg);
+}
+
+PyObject *
+PyStopIteration_New(PyObject *value)
+{
+    return PyObject_CallFunctionObjArgs(PyExc_StopIteration, value, NULL);
+}
+
+ComplexExtendsException(PyExc_Exception, StopIteration, StopIteration,
+    StopIteration_dealloc, 0, StopIteration_members, 0,
+    "Signal the end from iterator.__next__().");
 
 
 /*
diff -r 3a4b983dd70b -r 79088efb6c91 Objects/frameobject.c
--- a/Objects/frameobject.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Objects/frameobject.c	Sun Jul 10 01:09:48 2011 +1000
@@ -15,11 +15,12 @@
 #define OFF(x) offsetof(PyFrameObject, x)
 
 static PyMemberDef frame_memberlist[] = {
-    {"f_back",          T_OBJECT,       OFF(f_back),    READONLY},
-    {"f_code",          T_OBJECT,       OFF(f_code),    READONLY},
-    {"f_builtins",      T_OBJECT,       OFF(f_builtins),READONLY},
-    {"f_globals",       T_OBJECT,       OFF(f_globals), READONLY},
-    {"f_lasti",         T_INT,          OFF(f_lasti),   READONLY},
+    {"f_back",          T_OBJECT,       OFF(f_back),      READONLY},
+    {"f_code",          T_OBJECT,       OFF(f_code),      READONLY},
+    {"f_builtins",      T_OBJECT,       OFF(f_builtins),  READONLY},
+    {"f_globals",       T_OBJECT,       OFF(f_globals),   READONLY},
+    {"f_lasti",         T_INT,          OFF(f_lasti),     READONLY},
+    {"f_yieldfrom",     T_OBJECT,       OFF(f_yieldfrom), READONLY},
     {NULL}      /* Sentinel */
 };
 
@@ -444,6 +445,7 @@
     Py_CLEAR(f->f_exc_type);
     Py_CLEAR(f->f_exc_value);
     Py_CLEAR(f->f_exc_traceback);
+    Py_CLEAR(f->f_yieldfrom);
 
     co = f->f_code;
     if (co->co_zombieframe == NULL)
@@ -475,6 +477,7 @@
     Py_VISIT(f->f_exc_type);
     Py_VISIT(f->f_exc_value);
     Py_VISIT(f->f_exc_traceback);
+    Py_VISIT(f->f_yieldfrom);
 
     /* locals */
     slots = f->f_code->co_nlocals + PyTuple_GET_SIZE(f->f_code->co_cellvars) + PyTuple_GET_SIZE(f->f_code->co_freevars);
@@ -508,6 +511,7 @@
     Py_CLEAR(f->f_exc_value);
     Py_CLEAR(f->f_exc_traceback);
     Py_CLEAR(f->f_trace);
+    Py_CLEAR(f->f_yieldfrom);
 
     /* locals */
     slots = f->f_code->co_nlocals + PyTuple_GET_SIZE(f->f_code->co_cellvars) + PyTuple_GET_SIZE(f->f_code->co_freevars);
@@ -711,6 +715,7 @@
     f->f_lasti = -1;
     f->f_lineno = code->co_firstlineno;
     f->f_iblock = 0;
+    f->f_yieldfrom = NULL;
 
     _PyObject_GC_TRACK(f);
     return f;
diff -r 3a4b983dd70b -r 79088efb6c91 Objects/genobject.c
--- a/Objects/genobject.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Objects/genobject.c	Sun Jul 10 01:09:48 2011 +1000
@@ -5,6 +5,9 @@
 #include "structmember.h"
 #include "opcode.h"
 
+static PyObject *gen_close(PyGenObject *gen, PyObject *args);
+static void gen_undelegate(PyGenObject *);
+
 static int
 gen_traverse(PyGenObject *gen, visitproc visit, void *arg)
 {
@@ -90,12 +93,15 @@
 
     /* If the generator just returned (as opposed to yielding), signal
      * that the generator is exhausted. */
-    if (result == Py_None && f->f_stacktop == NULL) {
+    if (result && f->f_stacktop == NULL) {
+        if (result == Py_None)
+            PyErr_SetNone(PyExc_StopIteration);
+        else {
+            PyObject *e = PyStopIteration_New(result);
+            PyErr_SetObject(PyExc_StopIteration, e);
+        }
         Py_DECREF(result);
         result = NULL;
-        /* Set exception if not called by gen_iternext() */
-        if (arg)
-            PyErr_SetNone(PyExc_StopIteration);
     }
 
     if (!result || f->f_stacktop == NULL) {
@@ -114,17 +120,82 @@
 static PyObject *
 gen_send(PyGenObject *gen, PyObject *arg)
 {
-    return gen_send_ex(gen, arg, 0);
+    int exc = 0;
+    PyObject *ret;
+    PyObject *yf = gen->gi_frame ? gen->gi_frame->f_yieldfrom : NULL;
+    Py_INCREF(arg);
+    if (yf) {
+        Py_INCREF(yf);
+        if (PyGen_CheckExact(yf))
+            ret = gen_send((PyGenObject *)yf, arg);
+        else {
+            if (arg == Py_None)
+                ret = PyIter_Next(yf);
+            else
+                ret = PyObject_CallMethod(yf, "send", "O", arg);
+        }
+        if (ret) {
+            Py_DECREF(yf);
+            goto done;
+        }
+        gen_undelegate(gen);
+        Py_DECREF(arg);
+        arg = NULL;
+        if (PyGen_FetchStopIterationValue(&arg) < 0)
+            exc = 1;
+        Py_DECREF(yf);
+    }
+    ret = gen_send_ex(gen, arg, exc);
+done:
+    Py_XDECREF(arg);
+    return ret;
 }
 
 PyDoc_STRVAR(close_doc,
 "close(arg) -> raise GeneratorExit inside generator.");
 
+/*
+ *   This helper function is used by gen_close and gen_throw to
+ *   close a subiterator being delegated to by yield-from.
+ */
+
+static int
+gen_close_iter(PyObject *yf) {
+    PyObject *retval = NULL;
+    
+    if (PyGen_CheckExact(yf)) {
+        retval = gen_close((PyGenObject *)yf, NULL);
+        if (!retval)
+            return -1;
+    }
+    else {
+        PyObject *meth = PyObject_GetAttrString(yf, "close");
+        if (meth) {
+            retval = PyObject_CallFunction(meth, "");
+            Py_DECREF(meth);
+            if (!retval)
+                return -1;
+        }
+    }
+    Py_XDECREF(retval);
+    return 0;
+}	
+
 static PyObject *
 gen_close(PyGenObject *gen, PyObject *args)
 {
     PyObject *retval;
-    PyErr_SetNone(PyExc_GeneratorExit);
+    PyObject *yf = gen->gi_frame ? gen->gi_frame->f_yieldfrom : NULL;
+    int err = 0;
+
+    if (yf) {
+        Py_INCREF(yf);
+        err = gen_close_iter(yf);
+        gen_undelegate(gen);
+        Py_DECREF(yf);
+    }
+    if (err == 0)
+        PyErr_SetNone(PyExc_GeneratorExit);
     retval = gen_send_ex(gen, Py_None, 1);
     if (retval) {
         Py_DECREF(retval);
@@ -215,10 +286,51 @@
     PyObject *typ;
     PyObject *tb = NULL;
     PyObject *val = NULL;
+    PyObject *yf = gen->gi_frame ? gen->gi_frame->f_yieldfrom : NULL;
 
     if (!PyArg_UnpackTuple(args, "throw", 1, 3, &typ, &val, &tb))
         return NULL;
 
+    if (yf) {
+        PyObject *ret;
+        int err;
+        Py_INCREF(yf);
+        if (PyErr_GivenExceptionMatches(typ, PyExc_GeneratorExit)) {
+            err = gen_close_iter(yf);
+            Py_DECREF(yf);
+            gen_undelegate(gen);
+            if (err < 0)
+                return gen_send_ex(gen, Py_None, 1);
+            goto throw_here;
+        }
+        if (PyGen_CheckExact(yf))
+            ret = gen_throw((PyGenObject *)yf, args);
+        else {
+            PyObject *meth = PyObject_GetAttrString(yf, "throw");
+            if (!meth) {
+                PyErr_Clear();
+                Py_DECREF(yf);
+                gen_undelegate(gen);
+                goto throw_here;
+            }
+            ret = PyObject_CallObject(meth, args);
+            Py_DECREF(meth);
+        }
+        Py_DECREF(yf);
+        if (!ret) {
+            PyObject *val;
+            gen_undelegate(gen);
+            if (PyGen_FetchStopIterationValue(&val) == 0) {
+                ret = gen_send_ex(gen, val, 0);
+                Py_DECREF(val);
+            }
+            else
+                ret = gen_send_ex(gen, Py_None, 1);
+        }
+        return ret;
+    }
+
+throw_here:
     /* First, check the traceback argument, replacing None with
        NULL. */
     if (tb == Py_None)
@@ -276,9 +388,74 @@
 static PyObject *
 gen_iternext(PyGenObject *gen)
 {
-    return gen_send_ex(gen, NULL, 0);
+    PyObject *val = NULL;
+    PyObject *ret;
+    int exc = 0;
+    PyObject *yf = gen->gi_frame ? gen->gi_frame->f_yieldfrom : NULL;
+    if (yf) {
+        Py_INCREF(yf);
+        /* ceval.c ensures that yf is an iterator */
+        ret = yf->ob_type->tp_iternext(yf);
+        if (ret) {
+            Py_DECREF(yf);
+            return ret;
+        }
+        gen_undelegate(gen);
+        if (PyGen_FetchStopIterationValue(&val) < 0)
+            exc = 1;
+        Py_DECREF(yf);
+    }
+    ret = gen_send_ex(gen, val, exc);
+    Py_XDECREF(val);
+    return ret;
 }
 
+/*
+ *   In certain recursive situations, a generator may lose its frame
+ *   before we get a chance to clear f_yieldfrom, so we use this
+ *   helper function.
+ */
+
+static void
+gen_undelegate(PyGenObject *gen) {
+    if (gen->gi_frame) {
+        Py_XDECREF(gen->gi_frame->f_yieldfrom);
+        gen->gi_frame->f_yieldfrom = NULL;
+    }
+}
+
+/*
+ *   If StopIteration exception is set, fetches its 'value'
+ *   attribute if any, otherwise sets pvalue to None.
+ *
+ *   Returns 0 if no exception or StopIteration is set.
+ *   If any other exception is set, returns -1 and leaves
+ *   pvalue unchanged.
+ */
+
+int
+PyGen_FetchStopIterationValue(PyObject **pvalue) {
+    PyObject *et, *ev, *tb;
+    PyObject *value = NULL;
+    
+    if (PyErr_ExceptionMatches(PyExc_StopIteration)) {
+        PyErr_Fetch(&et, &ev, &tb);
+        Py_XDECREF(et); Py_XDECREF(tb);
+        if (ev) {
+            value = ((PyStopIterationObject *)ev)->value;
+            Py_XINCREF(value);
+            Py_DECREF(ev);
+        }
+    }
+    else if (PyErr_Occurred())
+        return -1;
+    if (!value) {
+        value = Py_None;
+        Py_INCREF(value);
+    }
+    *pvalue = value;
+    return 0;
+}
 
 static PyObject *
 gen_repr(PyGenObject *gen)
diff -r 3a4b983dd70b -r 79088efb6c91 Parser/Python.asdl
--- a/Parser/Python.asdl	Sat Jul 09 11:48:50 2011 +0200
+++ b/Parser/Python.asdl	Sun Jul 10 01:09:48 2011 +1000
@@ -59,7 +59,7 @@
 	     | DictComp(expr key, expr value, comprehension* generators)
 	     | GeneratorExp(expr elt, comprehension* generators)
 	     -- the grammar constrains where yield expressions can occur
-	     | Yield(expr? value)
+	     | Yield(int is_from, expr? value)
 	     -- need sequences for compare to distinguish between
 	     -- x < 4 < 3 and (x < 4) < 3
 	     | Compare(expr left, cmpop* ops, expr* comparators)
diff -r 3a4b983dd70b -r 79088efb6c91 Python/Python-ast.c
--- a/Python/Python-ast.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Python/Python-ast.c	Sun Jul 10 01:09:48 2011 +1000
@@ -205,6 +205,7 @@
 };
 static PyTypeObject *Yield_type;
 static char *Yield_fields[]={
+        "is_from",
         "value",
 };
 static PyTypeObject *Compare_type;
@@ -732,7 +733,7 @@
         GeneratorExp_type = make_type("GeneratorExp", expr_type,
                                       GeneratorExp_fields, 2);
         if (!GeneratorExp_type) return 0;
-        Yield_type = make_type("Yield", expr_type, Yield_fields, 1);
+        Yield_type = make_type("Yield", expr_type, Yield_fields, 2);
         if (!Yield_type) return 0;
         Compare_type = make_type("Compare", expr_type, Compare_fields, 3);
         if (!Compare_type) return 0;
@@ -1669,13 +1670,14 @@
 }
 
 expr_ty
-Yield(expr_ty value, int lineno, int col_offset, PyArena *arena)
+Yield(int is_from, expr_ty value, int lineno, int col_offset, PyArena *arena)
 {
         expr_ty p;
         p = (expr_ty)PyArena_Malloc(arena, sizeof(*p));
         if (!p)
                 return NULL;
         p->kind = Yield_kind;
+        p->v.Yield.is_from = is_from;
         p->v.Yield.value = value;
         p->lineno = lineno;
         p->col_offset = col_offset;
@@ -2717,6 +2719,11 @@
         case Yield_kind:
                 result = PyType_GenericNew(Yield_type, NULL, NULL);
                 if (!result) goto failed;
+                value = ast2obj_int(o->v.Yield.is_from);
+                if (!value) goto failed;
+                if (PyObject_SetAttrString(result, "is_from", value) == -1)
+                        goto failed;
+                Py_DECREF(value);
                 value = ast2obj_expr(o->v.Yield.value);
                 if (!value) goto failed;
                 if (PyObject_SetAttrString(result, "value", value) == -1)
@@ -5259,8 +5266,21 @@
                 return 1;
         }
         if (isinstance) {
+                int is_from;
                 expr_ty value;
 
+                if (PyObject_HasAttrString(obj, "is_from")) {
+                        int res;
+                        tmp = PyObject_GetAttrString(obj, "is_from");
+                        if (tmp == NULL) goto failed;
+                        res = obj2ast_int(tmp, &is_from, arena);
+                        if (res != 0) goto failed;
+                        Py_XDECREF(tmp);
+                        tmp = NULL;
+                } else {
+                        PyErr_SetString(PyExc_TypeError, "required field \"is_from\" missing from Yield");
+                        return 1;
+                }
                 if (PyObject_HasAttrString(obj, "value")) {
                         int res;
                         tmp = PyObject_GetAttrString(obj, "value");
@@ -5272,7 +5292,7 @@
                 } else {
                         value = NULL;
                 }
-                *out = Yield(value, lineno, col_offset, arena);
+                *out = Yield(is_from, value, lineno, col_offset, arena);
                 if (*out == NULL) goto failed;
                 return 0;
         }
diff -r 3a4b983dd70b -r 79088efb6c91 Python/ast.c
--- a/Python/ast.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Python/ast.c	Sun Jul 10 01:09:48 2011 +1000
@@ -1895,13 +1895,28 @@
             }
             return ast_for_binop(c, n);
         case yield_expr: {
+            node *an = NULL;
+            node *en = NULL;
+            int is_from = 0;
             expr_ty exp = NULL;
-            if (NCH(n) == 2) {
-                exp = ast_for_testlist(c, CHILD(n, 1));
+            if (NCH(n) > 1)
+                an = CHILD(n, 1); /* yield_arg */
+            if (an) {
+                en = CHILD(an, NCH(an) - 1);
+                if (NCH(an) == 2) {
+                    is_from = 1;
+                    exp = ast_for_expr(c, en);
+                }
+                else
+                    exp = ast_for_testlist(c, en);
                 if (!exp)
                     return NULL;
             }
-            return Yield(exp, LINENO(n), n->n_col_offset, c->c_arena);
+            return Yield(is_from, exp, LINENO(n), n->n_col_offset, c->c_arena);
+        }
+        case yield_from: {
+            expr_ty exp = ast_for_expr(c, CHILD(n, 2));
+            return Yield(1, exp, LINENO(n), n->n_col_offset, c->c_arena);
         }
         case factor:
             if (NCH(n) == 1) {
@@ -1925,7 +1940,7 @@
     /*
       arglist: (argument ',')* (argument [',']| '*' test [',' '**' test]
                | '**' test)
-      argument: [test '='] test [comp_for]        # Really [keyword '='] test
+      argument: [test '='] (test | yield_from) [comp_for]        # Really [keyword '='] test
     */
 
     int i, nargs, nkeywords, ngens;
@@ -2219,7 +2234,7 @@
       continue_stmt: 'continue'
       return_stmt: 'return' [testlist]
       yield_stmt: yield_expr
-      yield_expr: 'yield' testlist
+      yield_expr: 'yield' testlist | 'yield' 'from' test
       raise_stmt: 'raise' [test [',' test [',' test]]]
     */
     node *ch;
diff -r 3a4b983dd70b -r 79088efb6c91 Python/ceval.c
--- a/Python/ceval.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Python/ceval.c	Sun Jul 10 01:09:48 2011 +1000
@@ -1829,8 +1829,47 @@
             why = WHY_RETURN;
             goto fast_block_end;
 
+        TARGET(YIELD_FROM)
+            u = POP();
+            x = PyObject_GetIter(u);
+            Py_DECREF(u);
+            if (!x)
+                break;
+            /* x is now the iterator, make the first next() call */
+            retval = (*x->ob_type->tp_iternext)(x);
+            if (!retval) {
+                /* iter may be exhausted */
+                Py_DECREF(x);
+                if (PyErr_ExceptionMatches(PyExc_StopIteration)) {
+                    /* try to get return value from exception */
+                    PyObject *et, *ev, *tb;
+                    PyErr_Fetch(&et, &ev, &tb);
+                    Py_XDECREF(et); Py_XDECREF(tb);
+                    u = NULL;
+                    if (ev) {
+                        u = PyObject_GetAttrString(ev, "value");
+                        Py_DECREF(ev);
+                        if (!u) PyErr_Clear();
+                    }
+                    if (!u) {
+                        u = Py_None;
+                        Py_INCREF(u);
+                    }
+                    /* u is return value */
+                    PUSH(u);
+                    continue;
+                }
+                /* some other exception */
+                x = NULL;
+                break;
+            }
+            /* x is iterator, retval is value to be yielded */
+            f->f_yieldfrom = x;
+            goto yield_retval;
+
         TARGET(YIELD_VALUE)
             retval = POP();
+        yield_retval:
             f->f_stacktop = stack_pointer;
             why = WHY_YIELD;
             goto fast_yield;
diff -r 3a4b983dd70b -r 79088efb6c91 Python/compile.c
--- a/Python/compile.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Python/compile.c	Sun Jul 10 01:09:48 2011 +1000
@@ -763,6 +763,7 @@
         case IMPORT_STAR:
             return -1;
         case YIELD_VALUE:
+        case YIELD_FROM:
             return 0;
 
         case POP_BLOCK:
@@ -3202,7 +3203,12 @@
         else {
             ADDOP_O(c, LOAD_CONST, Py_None, consts);
         }
-        ADDOP(c, YIELD_VALUE);
+        if (e->v.Yield.is_from) {
+            ADDOP(c, YIELD_FROM);
+        }
+        else {
+            ADDOP(c, YIELD_VALUE);
+        }
         break;
     case Compare_kind:
         return compiler_compare(c, e);
diff -r 3a4b983dd70b -r 79088efb6c91 Python/graminit.c
--- a/Python/graminit.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Python/graminit.c	Sun Jul 10 01:09:48 2011 +1000
@@ -1700,29 +1700,36 @@
     {1, arcs_74_6},
     {2, arcs_74_7},
 };
-static arc arcs_75_0[1] = {
+static arc arcs_75_0[2] = {
     {24, 1},
+    {164, 2},
 };
 static arc arcs_75_1[3] = {
-    {158, 2},
-    {29, 3},
+    {158, 3},
+    {29, 4},
     {0, 1},
 };
-static arc arcs_75_2[1] = {
+static arc arcs_75_2[2] = {
+    {158, 3},
     {0, 2},
 };
 static arc arcs_75_3[1] = {
-    {24, 2},
+    {0, 3},
 };
-static state states_75[4] = {
-    {1, arcs_75_0},
+static arc arcs_75_4[2] = {
+    {24, 3},
+    {164, 3},
+};
+static state states_75[5] = {
+    {2, arcs_75_0},
     {3, arcs_75_1},
-    {1, arcs_75_2},
+    {2, arcs_75_2},
     {1, arcs_75_3},
+    {2, arcs_75_4},
 };
 static arc arcs_76_0[2] = {
     {158, 1},
-    {165, 1},
+    {166, 1},
 };
 static arc arcs_76_1[1] = {
     {0, 1},
@@ -1744,7 +1751,7 @@
     {107, 4},
 };
 static arc arcs_77_4[2] = {
-    {164, 5},
+    {165, 5},
     {0, 4},
 };
 static arc arcs_77_5[1] = {
@@ -1765,7 +1772,7 @@
     {109, 2},
 };
 static arc arcs_78_2[2] = {
-    {164, 3},
+    {165, 3},
     {0, 2},
 };
 static arc arcs_78_3[1] = {
@@ -1788,10 +1795,10 @@
     {1, arcs_79_1},
 };
 static arc arcs_80_0[1] = {
-    {167, 1},
+    {168, 1},
 };
 static arc arcs_80_1[2] = {
-    {9, 2},
+    {169, 2},
     {0, 1},
 };
 static arc arcs_80_2[1] = {
@@ -1802,171 +1809,208 @@
     {2, arcs_80_1},
     {1, arcs_80_2},
 };
-static dfa dfas[81] = {
+static arc arcs_81_0[2] = {
+    {73, 1},
+    {9, 2},
+};
+static arc arcs_81_1[1] = {
+    {24, 2},
+};
+static arc arcs_81_2[1] = {
+    {0, 2},
+};
+static state states_81[3] = {
+    {2, arcs_81_0},
+    {1, arcs_81_1},
+    {1, arcs_81_2},
+};
+static arc arcs_82_0[1] = {
+    {168, 1},
+};
+static arc arcs_82_1[1] = {
+    {73, 2},
+};
+static arc arcs_82_2[1] = {
+    {24, 3},
+};
+static arc arcs_82_3[1] = {
+    {0, 3},
+};
+static state states_82[4] = {
+    {1, arcs_82_0},
+    {1, arcs_82_1},
+    {1, arcs_82_2},
+    {1, arcs_82_3},
+};
+static dfa dfas[83] = {
     {256, "single_input", 0, 3, states_0,
-     "\004\050\060\200\000\000\000\240\340\223\160\220\045\200\020\000\000\206\120\076\204"},
+     "\004\050\060\200\000\000\000\240\340\223\160\220\045\200\020\000\000\206\120\076\004\001"},
     {257, "file_input", 0, 2, states_1,
-     "\204\050\060\200\000\000\000\240\340\223\160\220\045\200\020\000\000\206\120\076\204"},
+     "\204\050\060\200\000\000\000\240\340\223\160\220\045\200\020\000\000\206\120\076\004\001"},
     {258, "eval_input", 0, 3, states_2,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
+     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000\000"},
     {259, "decorator", 0, 7, states_3,
-     "\000\010\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\010\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {260, "decorators", 0, 2, states_4,
-     "\000\010\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\010\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {261, "decorated", 0, 3, states_5,
-     "\000\010\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\010\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {262, "funcdef", 0, 8, states_6,
-     "\000\000\020\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\000\020\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {263, "parameters", 0, 4, states_7,
-     "\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {264, "typedargslist", 0, 18, states_8,
-     "\000\000\040\200\001\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\000\040\200\001\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {265, "tfpdef", 0, 4, states_9,
-     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {266, "varargslist", 0, 18, states_10,
-     "\000\000\040\200\001\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\000\040\200\001\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {267, "vfpdef", 0, 2, states_11,
-     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
+     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
     {268, "stmt", 0, 2, states_12,
-     "\000\050\060\200\000\000\000\240\340\223\160\220\045\200\020\000\000\206\120\076\204"},
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-     "\000\040\040\200\000\000\000\240\340\223\160\000\000\200\020\000\000\206\120\076\200"},
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-     "\000\000\000\000\000\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\200"},
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-     "\000\000\000\000\000\000\000\000\000\001\000\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\022\000\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\020\000\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\002\000\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
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     {288, "dotted_as_names", 0, 2, states_32,
-     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
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     {290, "global_stmt", 0, 3, states_34,
-     "\000\000\000\000\000\000\000\000\000\000\020\000\000\000\000\000\000\000\000\000\000"},
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     {291, "nonlocal_stmt", 0, 3, states_35,
-     "\000\000\000\000\000\000\000\000\000\000\040\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\100\000\000\000\000\000\000\000\000\000\000"},
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-     "\000\010\020\000\000\000\000\000\000\000\000\220\045\000\000\000\000\000\000\000\004"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\020\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\200\000\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\000\001\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\000\004\000\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\000\040\000\000\000\000\000\000\000\000"},
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-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\000\000\001\000\000\000\000\000\000\000"},
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-     "\004\040\040\200\000\000\000\240\340\223\160\000\000\200\020\000\000\206\120\076\200"},
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-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\000\000\200\000\000\000\000\000\000\000"},
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-     "\000\000\000\000\000\000\000\000\000\000\000\000\000\200\000\000\000\000\000\000\000"},
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     {306, "or_test", 0, 2, states_50,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\020\000\000\206\120\076\000"},
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-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\020\000\000\206\120\076\000"},
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     {308, "not_test", 0, 3, states_52,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\020\000\000\206\120\076\000"},
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     {309, "comparison", 0, 2, states_53,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {310, "comp_op", 0, 4, states_54,
-     "\000\000\000\000\000\000\000\000\000\000\000\000\002\000\220\177\000\000\000\000\000"},
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     {311, "star_expr", 0, 3, states_55,
-     "\000\000\000\200\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
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     {312, "expr", 0, 2, states_56,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {313, "xor_expr", 0, 2, states_57,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {314, "and_expr", 0, 2, states_58,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {315, "shift_expr", 0, 2, states_59,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {316, "arith_expr", 0, 2, states_60,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {317, "term", 0, 2, states_61,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {318, "factor", 0, 3, states_62,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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     {319, "power", 0, 4, states_63,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\000\120\076\000"},
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     {320, "atom", 0, 9, states_64,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\000\000\000\000\000\120\076\000"},
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-     "\000\040\040\200\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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     {322, "trailer", 0, 7, states_66,
-     "\000\040\000\000\000\000\000\000\000\100\000\000\000\000\000\000\000\000\020\000\000"},
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     {323, "subscriptlist", 0, 3, states_67,
-     "\000\040\040\002\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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     {324, "subscript", 0, 5, states_68,
-     "\000\040\040\002\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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     {325, "sliceop", 0, 3, states_69,
-     "\000\000\000\002\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
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     {326, "exprlist", 0, 3, states_70,
-     "\000\040\040\200\000\000\000\000\000\200\000\000\000\000\000\000\000\206\120\076\000"},
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-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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     {328, "dictorsetmaker", 0, 11, states_72,
-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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     {329, "classdef", 0, 8, states_73,
-     "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\004"},
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     {330, "arglist", 0, 8, states_74,
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-     "\000\040\040\000\000\000\000\000\000\200\000\000\000\200\020\000\000\206\120\076\000"},
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     {332, "comp_iter", 0, 2, states_76,
-     "\000\000\000\000\000\000\000\000\000\000\000\020\001\000\000\000\000\000\000\000\000"},
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     {333, "comp_for", 0, 6, states_77,
-     "\000\000\000\000\000\000\000\000\000\000\000\000\001\000\000\000\000\000\000\000\000"},
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     {334, "comp_if", 0, 4, states_78,
-     "\000\000\000\000\000\000\000\000\000\000\000\020\000\000\000\000\000\000\000\000\000"},
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     {335, "encoding_decl", 0, 2, states_79,
-     "\000\000\040\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"},
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     {336, "yield_expr", 0, 3, states_80,
-     "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\200"},
+     "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001"},
+    {337, "yield_arg", 0, 3, states_81,
+     "\000\040\040\000\000\000\000\000\000\202\000\000\000\200\020\000\000\206\120\076\000\000"},
+    {338, "yield_from", 0, 4, states_82,
+     "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\001"},
 };
-static label labels[168] = {
+static label labels[170] = {
     {0, "EMPTY"},
     {256, 0},
     {4, 0},
@@ -2131,14 +2175,16 @@
     {325, 0},
     {1, "class"},
     {331, 0},
+    {338, 0},
     {332, 0},
     {334, 0},
     {335, 0},
     {1, "yield"},
+    {337, 0},
 };
 grammar _PyParser_Grammar = {
-    81,
+    83,
     dfas,
-    {168, labels},
+    {170, labels},
     256
 };
diff -r 3a4b983dd70b -r 79088efb6c91 Python/opcode_targets.h
--- a/Python/opcode_targets.h	Sat Jul 09 11:48:50 2011 +0200
+++ b/Python/opcode_targets.h	Sun Jul 10 01:09:48 2011 +1000
@@ -71,7 +71,7 @@
     &&TARGET_STORE_LOCALS,
     &&TARGET_PRINT_EXPR,
     &&TARGET_LOAD_BUILD_CLASS,
-    &&_unknown_opcode,
+    &&TARGET_YIELD_FROM,
     &&_unknown_opcode,
     &&_unknown_opcode,
     &&TARGET_INPLACE_LSHIFT,
diff -r 3a4b983dd70b -r 79088efb6c91 Python/symtable.c
--- a/Python/symtable.c	Sat Jul 09 11:48:50 2011 +0200
+++ b/Python/symtable.c	Sun Jul 10 01:09:48 2011 +1000
@@ -1133,14 +1133,6 @@
         if (s->v.Return.value) {
             VISIT(st, expr, s->v.Return.value);
             st->st_cur->ste_returns_value = 1;
-            if (st->st_cur->ste_generator) {
-                PyErr_SetString(PyExc_SyntaxError,
-                    RETURN_VAL_IN_GENERATOR);
-                PyErr_SyntaxLocationEx(st->st_filename,
-                                       s->lineno,
-                                       s->col_offset);
-                return 0;
-            }
         }
         break;
     case Delete_kind:
@@ -1342,13 +1334,6 @@
         if (e->v.Yield.value)
             VISIT(st, expr, e->v.Yield.value);
         st->st_cur->ste_generator = 1;
-        if (st->st_cur->ste_returns_value) {
-            PyErr_SetString(PyExc_SyntaxError,
-                RETURN_VAL_IN_GENERATOR);
-            PyErr_SyntaxLocationEx(st->st_filename,
-                                   e->lineno, e->col_offset);
-            return 0;
-        }
         break;
     case Compare_kind:
         VISIT(st, expr, e->v.Compare.left);