PEP 343 -- the with-statement.

This was started by Mike Bland and completed by Guido
(with help from Neal).

This still needs a __future__ statement added;
Thomas is working on Michael's patch for that aspect.

There's a small amount of code cleanup and refactoring
in ast.c, compile.c and ceval.c (I fixed the lltrace
behavior when EXT_POP is used -- however I had to make
lltrace a static global).

6 files changed, 709 insertions, 52 deletions

diff --git a/Lib/compiler/ast.py b/Lib/compiler/ast.py
index accda45..e270995 100644
--- a/Lib/compiler/ast.py
+++ b/Lib/compiler/ast.py
@@ -553,7 +553,7 @@ class Function(Node):
             self.varargs = 1
         if flags & CO_VARKEYWORDS:
             self.kwargs = 1
-
+    
 
 
     def getChildren(self):
@@ -584,7 +584,7 @@ class GenExpr(Node):
         self.lineno = lineno
         self.argnames = ['[outmost-iterable]']
         self.varargs = self.kwargs = None
-
+    
 
 
     def getChildren(self):
@@ -763,7 +763,7 @@ class Lambda(Node):
             self.varargs = 1
         if flags & CO_VARKEYWORDS:
             self.kwargs = 1
-
+    
 
 
     def getChildren(self):
@@ -1297,6 +1297,31 @@ class While(Node):
     def __repr__(self):
         return "While(%s, %s, %s)" % (repr(self.test), repr(self.body), repr(self.else_))
 
+class With(Node):
+    def __init__(self, expr, vars, body, lineno=None):
+        self.expr = expr
+        self.vars = vars
+        self.body = body
+        self.lineno = lineno
+
+    def getChildren(self):
+        children = []
+        children.append(self.expr)
+        children.append(self.vars)
+        children.append(self.body)
+        return tuple(children)
+
+    def getChildNodes(self):
+        nodelist = []
+        nodelist.append(self.expr)
+        if self.vars is not None:
+            nodelist.append(self.vars)
+        nodelist.append(self.body)
+        return tuple(nodelist)
+
+    def __repr__(self):
+        return "With(%s, %s, %s)" % (repr(self.expr), repr(self.vars), repr(self.body))
+
 class Yield(Node):
     def __init__(self, value, lineno=None):
         self.value = value
diff --git a/Lib/opcode.py b/Lib/opcode.py
index 9517c43..095ca42 100644
--- a/Lib/opcode.py
+++ b/Lib/opcode.py
@@ -41,6 +41,7 @@ def jabs_op(name, op):
     hasjabs.append(op)
 
 # Instruction opcodes for compiled code
+# Blank lines correspond to available opcodes
 
 def_op('STOP_CODE', 0)
 def_op('POP_TOP', 1)
@@ -59,7 +60,6 @@ def_op('UNARY_INVERT', 15)
 
 def_op('LIST_APPEND', 18)
 def_op('BINARY_POWER', 19)
-
 def_op('BINARY_MULTIPLY', 20)
 def_op('BINARY_DIVIDE', 21)
 def_op('BINARY_MODULO', 22)
@@ -70,7 +70,6 @@ def_op('BINARY_FLOOR_DIVIDE', 26)
 def_op('BINARY_TRUE_DIVIDE', 27)
 def_op('INPLACE_FLOOR_DIVIDE', 28)
 def_op('INPLACE_TRUE_DIVIDE', 29)
-
 def_op('SLICE+0', 30)
 def_op('SLICE+1', 31)
 def_op('SLICE+2', 32)
@@ -93,7 +92,6 @@ def_op('INPLACE_DIVIDE', 58)
 def_op('INPLACE_MODULO', 59)
 def_op('STORE_SUBSCR', 60)
 def_op('DELETE_SUBSCR', 61)
-
 def_op('BINARY_LSHIFT', 62)
 def_op('BINARY_RSHIFT', 63)
 def_op('BINARY_AND', 64)
@@ -113,13 +111,12 @@ def_op('INPLACE_AND', 77)
 def_op('INPLACE_XOR', 78)
 def_op('INPLACE_OR', 79)
 def_op('BREAK_LOOP', 80)
-
+def_op('WITH_CLEANUP', 81)
 def_op('LOAD_LOCALS', 82)
 def_op('RETURN_VALUE', 83)
 def_op('IMPORT_STAR', 84)
 def_op('EXEC_STMT', 85)
 def_op('YIELD_VALUE', 86)
-
 def_op('POP_BLOCK', 87)
 def_op('END_FINALLY', 88)
 def_op('BUILD_CLASS', 89)
@@ -171,7 +168,6 @@ def_op('RAISE_VARARGS', 130)    # Number of raise arguments (1, 2, or 3)
 def_op('CALL_FUNCTION', 131)    # #args + (#kwargs << 8)
 def_op('MAKE_FUNCTION', 132)    # Number of args with default values
 def_op('BUILD_SLICE', 133)      # Number of items
-
 def_op('MAKE_CLOSURE', 134)
 def_op('LOAD_CLOSURE', 135)
 hasfree.append(135)
@@ -183,7 +179,6 @@ hasfree.append(137)
 def_op('CALL_FUNCTION_VAR', 140)     # #args + (#kwargs << 8)
 def_op('CALL_FUNCTION_KW', 141)      # #args + (#kwargs << 8)
 def_op('CALL_FUNCTION_VAR_KW', 142)  # #args + (#kwargs << 8)
-
 def_op('EXTENDED_ARG', 143)
 EXTENDED_ARG = 143
 
diff --git a/Lib/symbol.py b/Lib/symbol.py
index dd83740..c650138 100755
--- a/Lib/symbol.py
+++ b/Lib/symbol.py
@@ -50,48 +50,50 @@ if_stmt = 292
 while_stmt = 293
 for_stmt = 294
 try_stmt = 295
-except_clause = 296
-suite = 297
-testlist_safe = 298
-old_test = 299
-old_lambdef = 300
-test = 301
-or_test = 302
-and_test = 303
-not_test = 304
-comparison = 305
-comp_op = 306
-expr = 307
-xor_expr = 308
-and_expr = 309
-shift_expr = 310
-arith_expr = 311
-term = 312
-factor = 313
-power = 314
-atom = 315
-listmaker = 316
-testlist_gexp = 317
-lambdef = 318
-trailer = 319
-subscriptlist = 320
-subscript = 321
-sliceop = 322
-exprlist = 323
-testlist = 324
-dictmaker = 325
-classdef = 326
-arglist = 327
-argument = 328
-list_iter = 329
-list_for = 330
-list_if = 331
-gen_iter = 332
-gen_for = 333
-gen_if = 334
-testlist1 = 335
-encoding_decl = 336
-yield_expr = 337
+with_stmt = 296
+with_var = 297
+except_clause = 298
+suite = 299
+testlist_safe = 300
+old_test = 301
+old_lambdef = 302
+test = 303
+or_test = 304
+and_test = 305
+not_test = 306
+comparison = 307
+comp_op = 308
+expr = 309
+xor_expr = 310
+and_expr = 311
+shift_expr = 312
+arith_expr = 313
+term = 314
+factor = 315
+power = 316
+atom = 317
+listmaker = 318
+testlist_gexp = 319
+lambdef = 320
+trailer = 321
+subscriptlist = 322
+subscript = 323
+sliceop = 324
+exprlist = 325
+testlist = 326
+dictmaker = 327
+classdef = 328
+arglist = 329
+argument = 330
+list_iter = 331
+list_for = 332
+list_if = 333
+gen_iter = 334
+gen_for = 335
+gen_if = 336
+testlist1 = 337
+encoding_decl = 338
+yield_expr = 339
 #--end constants--
 
 sym_name = {}
diff --git a/Lib/test/contextmanager.py b/Lib/test/contextmanager.py
new file mode 100644
index 0000000..0ebf646
--- /dev/null
+++ b/Lib/test/contextmanager.py
@@ -0,0 +1,34 @@
+class GeneratorContextManager(object):
+    def __init__(self, gen):
+        self.gen = gen
+
+    def __context__(self):
+        return self
+
+    def __enter__(self):
+        try:
+            return self.gen.next()
+        except StopIteration:
+            raise RuntimeError("generator didn't yield")
+
+    def __exit__(self, type, value, traceback):
+        if type is None:
+            try:
+                self.gen.next()
+            except StopIteration:
+                return
+            else:
+                raise RuntimeError("generator didn't stop")
+        else:
+            try:
+                self.gen.throw(type, value, traceback)
+            except (type, StopIteration):
+                return
+            else:
+                raise RuntimeError("generator caught exception")
+
+def contextmanager(func):
+    def helper(*args, **kwds):
+        return GeneratorContextManager(func(*args, **kwds))
+    return helper
+
diff --git a/Lib/test/nested.py b/Lib/test/nested.py
new file mode 100644
index 0000000..bb210d4
--- /dev/null
+++ b/Lib/test/nested.py
@@ -0,0 +1,41 @@
+import sys
+from collections import deque
+
+
+class nested(object):
+    def __init__(self, *contexts):
+        self.contexts = contexts
+        self.entered = None
+
+    def __context__(self):
+        return self
+
+    def __enter__(self):
+        if self.entered is not None:
+            raise RuntimeError("Context is not reentrant")
+        self.entered = deque()
+        vars = []
+        try:
+            for context in self.contexts:
+                mgr = context.__context__()
+                vars.append(mgr.__enter__())
+                self.entered.appendleft(mgr)
+        except:
+            self.__exit__(*sys.exc_info())
+            raise
+        return vars
+
+    def __exit__(self, *exc_info):
+        # Behave like nested with statements
+        # first in, last out
+        # New exceptions override old ones
+        ex = exc_info
+        for mgr in self.entered:
+            try:
+                mgr.__exit__(*ex)
+            except:
+                ex = sys.exc_info()
+        self.entered = None
+        if ex is not exc_info:
+            raise ex[0], ex[1], ex[2]
+
diff --git a/Lib/test/test_with.py b/Lib/test/test_with.py
new file mode 100644
index 0000000..9d809ef
--- /dev/null
+++ b/Lib/test/test_with.py
@@ -0,0 +1,560 @@
+#!/usr/bin/env python
+
+"""Unit tests for the with statement specified in PEP 343."""
+
+__author__ = "Mike Bland"
+__email__ = "mbland at acm dot org"
+
+import unittest
+from test.contextmanager import GeneratorContextManager
+from test.nested import nested
+from test.test_support import run_unittest
+
+
+class MockContextManager(GeneratorContextManager):
+    def __init__(self, gen):
+        GeneratorContextManager.__init__(self, gen)
+        self.context_called = False
+        self.enter_called = False
+        self.exit_called = False
+        self.exit_args = None
+
+    def __context__(self):
+        self.context_called = True
+        return GeneratorContextManager.__context__(self)
+
+    def __enter__(self):
+        self.enter_called = True
+        return GeneratorContextManager.__enter__(self)
+
+    def __exit__(self, type, value, traceback):
+        self.exit_called = True
+        self.exit_args = (type, value, traceback)
+        return GeneratorContextManager.__exit__(self, type, value, traceback)
+
+
+def mock_contextmanager(func):
+    def helper(*args, **kwds):
+        return MockContextManager(func(*args, **kwds))
+    return helper
+
+
+class MockResource(object):
+    def __init__(self):
+        self.yielded = False
+        self.stopped = False
+
+
+@mock_contextmanager
+def mock_contextmanager_generator():
+    mock = MockResource()
+    try:
+        mock.yielded = True
+        yield mock
+    finally:
+        mock.stopped = True
+
+
+class MockNested(nested):
+    def __init__(self, *contexts):
+        nested.__init__(self, *contexts)
+        self.context_called = False
+        self.enter_called = False
+        self.exit_called = False
+        self.exit_args = None
+
+    def __context__(self):
+        self.context_called = True
+        return nested.__context__(self)
+
+    def __enter__(self):
+        self.enter_called = True
+        return nested.__enter__(self)
+
+    def __exit__(self, *exc_info):
+        self.exit_called = True
+        self.exit_args = exc_info
+        return nested.__exit__(self, *exc_info)
+
+ 
+class FailureTestCase(unittest.TestCase):
+    def testNameError(self):
+        def fooNotDeclared():
+            with foo: pass
+        self.assertRaises(NameError, fooNotDeclared)
+
+    def testContextAttributeError(self):
+        class LacksContext(object):
+            def __enter__(self):
+                pass
+
+            def __exit__(self, type, value, traceback):
+                pass
+
+        def fooLacksContext():
+            foo = LacksContext()
+            with foo: pass
+        self.assertRaises(AttributeError, fooLacksContext)
+
+    def testEnterAttributeError(self):
+        class LacksEnter(object):
+            def __context__(self):
+                pass
+
+            def __exit__(self, type, value, traceback):
+                pass
+
+        def fooLacksEnter():
+            foo = LacksEnter()
+            with foo: pass
+        self.assertRaises(AttributeError, fooLacksEnter)
+
+    def testExitAttributeError(self):
+        class LacksExit(object):
+            def __context__(self):
+                pass
+
+            def __enter__(self):
+                pass
+
+        def fooLacksExit():
+            foo = LacksExit()
+            with foo: pass
+        self.assertRaises(AttributeError, fooLacksExit)
+
+    def assertRaisesSyntaxError(self, codestr):
+        def shouldRaiseSyntaxError(s):
+            compile(s, '', 'single')
+        self.assertRaises(SyntaxError, shouldRaiseSyntaxError, codestr)
+
+    def testAssignmentToNoneError(self):
+        self.assertRaisesSyntaxError('with mock as None:\n  pass')
+        self.assertRaisesSyntaxError(
+            'with mock as (None):\n'
+            '  pass')
+
+    def testAssignmentToEmptyTupleError(self):
+        self.assertRaisesSyntaxError(
+            'with mock as ():\n'
+            '  pass')
+
+    def testAssignmentToTupleOnlyContainingNoneError(self):
+        self.assertRaisesSyntaxError('with mock as None,:\n  pass')
+        self.assertRaisesSyntaxError(
+            'with mock as (None,):\n'
+            '  pass')
+
+    def testAssignmentToTupleContainingNoneError(self):
+        self.assertRaisesSyntaxError(
+            'with mock as (foo, None, bar):\n'
+            '  pass')
+
+    def testContextThrows(self):
+        class ContextThrows(object):
+            def __context__(self):
+                raise RuntimeError("Context threw")
+
+        def shouldThrow():
+            ct = ContextThrows()
+            self.foo = None
+            with ct as self.foo:
+                pass
+        self.assertRaises(RuntimeError, shouldThrow)
+        self.assertEqual(self.foo, None)
+
+    def testEnterThrows(self):
+        class EnterThrows(object):
+            def __context__(self):
+                return self
+
+            def __enter__(self):
+                raise RuntimeError("Context threw")
+
+            def __exit__(self, *args):
+                pass
+
+        def shouldThrow():
+            ct = EnterThrows()
+            self.foo = None
+            with ct as self.foo:
+                pass
+        self.assertRaises(RuntimeError, shouldThrow)
+        self.assertEqual(self.foo, None)
+
+    def testExitThrows(self):
+        class ExitThrows(object):
+            def __context__(self):
+                return self
+            def __enter__(self):
+                return
+            def __exit__(self, *args):
+                raise RuntimeError(42)
+        def shouldThrow():
+            with ExitThrows():
+                pass
+        self.assertRaises(RuntimeError, shouldThrow)
+
+class ContextmanagerAssertionMixin(object):
+    TEST_EXCEPTION = RuntimeError("test exception")
+
+    def assertInWithManagerInvariants(self, mock_manager):
+        self.assertTrue(mock_manager.context_called)
+        self.assertTrue(mock_manager.enter_called)
+        self.assertFalse(mock_manager.exit_called)
+        self.assertEqual(mock_manager.exit_args, None)
+
+    def assertAfterWithManagerInvariants(self, mock_manager, exit_args):
+        self.assertTrue(mock_manager.context_called)
+        self.assertTrue(mock_manager.enter_called)
+        self.assertTrue(mock_manager.exit_called)
+        self.assertEqual(mock_manager.exit_args, exit_args)
+
+    def assertAfterWithManagerInvariantsNoError(self, mock_manager):
+        self.assertAfterWithManagerInvariants(mock_manager,
+            (None, None, None))
+
+    def assertInWithGeneratorInvariants(self, mock_generator):
+        self.assertTrue(mock_generator.yielded)
+        self.assertFalse(mock_generator.stopped)
+
+    def assertAfterWithGeneratorInvariantsNoError(self, mock_generator):
+        self.assertTrue(mock_generator.yielded)
+        self.assertTrue(mock_generator.stopped)
+
+    def raiseTestException(self):
+        raise self.TEST_EXCEPTION
+
+    def assertAfterWithManagerInvariantsWithError(self, mock_manager):
+        self.assertTrue(mock_manager.context_called)
+        self.assertTrue(mock_manager.enter_called)
+        self.assertTrue(mock_manager.exit_called)
+        self.assertEqual(mock_manager.exit_args[0], RuntimeError)
+        self.assertEqual(mock_manager.exit_args[1], self.TEST_EXCEPTION)
+
+    def assertAfterWithGeneratorInvariantsWithError(self, mock_generator):
+        self.assertTrue(mock_generator.yielded)
+        self.assertTrue(mock_generator.stopped)
+
+
+class NonexceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
+    def testInlineGeneratorSyntax(self):
+        with mock_contextmanager_generator():
+            pass
+
+    def testUnboundGenerator(self):
+        mock = mock_contextmanager_generator()
+        with mock:
+            pass
+        self.assertAfterWithManagerInvariantsNoError(mock)
+
+    def testInlineGeneratorBoundSyntax(self):
+        with mock_contextmanager_generator() as foo:
+            self.assertInWithGeneratorInvariants(foo)
+        # FIXME: In the future, we'll try to keep the bound names from leaking
+        self.assertAfterWithGeneratorInvariantsNoError(foo)
+
+    def testInlineGeneratorBoundToExistingVariable(self):
+        foo = None
+        with mock_contextmanager_generator() as foo:
+            self.assertInWithGeneratorInvariants(foo)
+        self.assertAfterWithGeneratorInvariantsNoError(foo)
+
+    def testInlineGeneratorBoundToDottedVariable(self):
+        with mock_contextmanager_generator() as self.foo:
+            self.assertInWithGeneratorInvariants(self.foo)
+        self.assertAfterWithGeneratorInvariantsNoError(self.foo)
+
+    def testBoundGenerator(self):
+        mock = mock_contextmanager_generator()
+        with mock as foo:
+            self.assertInWithGeneratorInvariants(foo)
+            self.assertInWithManagerInvariants(mock)
+        self.assertAfterWithGeneratorInvariantsNoError(foo)
+        self.assertAfterWithManagerInvariantsNoError(mock)
+
+    def testNestedSingleStatements(self):
+        mock_a = mock_contextmanager_generator()
+        with mock_a as foo:
+            mock_b = mock_contextmanager_generator()
+            with mock_b as bar:
+                self.assertInWithManagerInvariants(mock_a)
+                self.assertInWithManagerInvariants(mock_b)
+                self.assertInWithGeneratorInvariants(foo)
+                self.assertInWithGeneratorInvariants(bar)
+            self.assertAfterWithManagerInvariantsNoError(mock_b)
+            self.assertAfterWithGeneratorInvariantsNoError(bar)
+            self.assertInWithManagerInvariants(mock_a)
+            self.assertInWithGeneratorInvariants(foo)
+        self.assertAfterWithManagerInvariantsNoError(mock_a)
+        self.assertAfterWithGeneratorInvariantsNoError(foo)
+
+
+class NestedNonexceptionalTestCase(unittest.TestCase,
+    ContextmanagerAssertionMixin):
+    def testSingleArgInlineGeneratorSyntax(self):
+        with nested(mock_contextmanager_generator()):
+            pass
+
+    def testSingleArgUnbound(self):
+        mock_contextmanager = mock_contextmanager_generator()
+        mock_nested = MockNested(mock_contextmanager)
+        with mock_nested:
+            self.assertInWithManagerInvariants(mock_contextmanager)
+            self.assertInWithManagerInvariants(mock_nested)
+        self.assertAfterWithManagerInvariantsNoError(mock_contextmanager)
+        self.assertAfterWithManagerInvariantsNoError(mock_nested)
+
+    def testSingleArgBoundToNonTuple(self):
+        m = mock_contextmanager_generator()
+        # This will bind all the arguments to nested() into a single list
+        # assigned to foo.
+        with nested(m) as foo:
+            self.assertInWithManagerInvariants(m)
+        self.assertAfterWithManagerInvariantsNoError(m)
+
+    def testSingleArgBoundToSingleElementParenthesizedList(self):
+        m = mock_contextmanager_generator()
+        # This will bind all the arguments to nested() into a single list
+        # assigned to foo.
+        # FIXME: what should this do:  with nested(m) as (foo,):
+        with nested(m) as (foo):
+            self.assertInWithManagerInvariants(m)
+        self.assertAfterWithManagerInvariantsNoError(m)
+
+    def testSingleArgBoundToMultipleElementTupleError(self):
+        def shouldThrowValueError():
+            with nested(mock_contextmanager_generator()) as (foo, bar):
+                pass
+        self.assertRaises(ValueError, shouldThrowValueError)
+
+    def testSingleArgUnbound(self):
+        mock_contextmanager = mock_contextmanager_generator()
+        mock_nested = MockNested(mock_contextmanager)
+        with mock_nested:
+            self.assertInWithManagerInvariants(mock_contextmanager)
+            self.assertInWithManagerInvariants(mock_nested)
+        self.assertAfterWithManagerInvariantsNoError(mock_contextmanager)
+        self.assertAfterWithManagerInvariantsNoError(mock_nested)
+
+    def testMultipleArgUnbound(self):
+        m = mock_contextmanager_generator()
+        n = mock_contextmanager_generator()
+        o = mock_contextmanager_generator()
+        mock_nested = MockNested(m, n, o)
+        with mock_nested:
+            self.assertInWithManagerInvariants(m)
+            self.assertInWithManagerInvariants(n)
+            self.assertInWithManagerInvariants(o)
+            self.assertInWithManagerInvariants(mock_nested)
+        self.assertAfterWithManagerInvariantsNoError(m)
+        self.assertAfterWithManagerInvariantsNoError(n)
+        self.assertAfterWithManagerInvariantsNoError(o)
+        self.assertAfterWithManagerInvariantsNoError(mock_nested)
+
+    def testMultipleArgBound(self):
+        mock_nested = MockNested(mock_contextmanager_generator(),
+            mock_contextmanager_generator(), mock_contextmanager_generator())
+        with mock_nested as (m, n, o):
+            self.assertInWithGeneratorInvariants(m)
+            self.assertInWithGeneratorInvariants(n)
+            self.assertInWithGeneratorInvariants(o)
+            self.assertInWithManagerInvariants(mock_nested)
+        self.assertAfterWithGeneratorInvariantsNoError(m)
+        self.assertAfterWithGeneratorInvariantsNoError(n)
+        self.assertAfterWithGeneratorInvariantsNoError(o)
+        self.assertAfterWithManagerInvariantsNoError(mock_nested)
+
+
+class ExceptionalTestCase(unittest.TestCase, ContextmanagerAssertionMixin):
+    def testSingleResource(self):
+        cm = mock_contextmanager_generator()
+        def shouldThrow():
+            with cm as self.resource:
+                self.assertInWithManagerInvariants(cm)
+                self.assertInWithGeneratorInvariants(self.resource)
+                self.raiseTestException()
+        self.assertRaises(RuntimeError, shouldThrow)
+        self.assertAfterWithManagerInvariantsWithError(cm)
+        self.assertAfterWithGeneratorInvariantsWithError(self.resource)
+
+    def testNestedSingleStatements(self):
+        mock_a = mock_contextmanager_generator()
+        mock_b = mock_contextmanager_generator()
+        def shouldThrow():
+            with mock_a as self.foo:
+                with mock_b as self.bar:
+                    self.assertInWithManagerInvariants(mock_a)
+                    self.assertInWithManagerInvariants(mock_b)
+                    self.assertInWithGeneratorInvariants(self.foo)
+                    self.assertInWithGeneratorInvariants(self.bar)
+                    self.raiseTestException()
+        self.assertRaises(RuntimeError, shouldThrow)
+        self.assertAfterWithManagerInvariantsWithError(mock_a)
+        self.assertAfterWithManagerInvariantsWithError(mock_b)
+        self.assertAfterWithGeneratorInvariantsWithError(self.foo)
+        self.assertAfterWithGeneratorInvariantsWithError(self.bar)
+
+    def testMultipleResourcesInSingleStatement(self):
+        cm_a = mock_contextmanager_generator()
+        cm_b = mock_contextmanager_generator()
+        mock_nested = MockNested(cm_a, cm_b)
+        def shouldThrow():
+            with mock_nested as (self.resource_a, self.resource_b):
+                self.assertInWithManagerInvariants(cm_a)
+                self.assertInWithManagerInvariants(cm_b)
+                self.assertInWithManagerInvariants(mock_nested)
+                self.assertInWithGeneratorInvariants(self.resource_a)
+                self.assertInWithGeneratorInvariants(self.resource_b)
+                self.raiseTestException()
+        self.assertRaises(RuntimeError, shouldThrow)
+        self.assertAfterWithManagerInvariantsWithError(cm_a)
+        self.assertAfterWithManagerInvariantsWithError(cm_b)
+        self.assertAfterWithManagerInvariantsWithError(mock_nested)
+        self.assertAfterWithGeneratorInvariantsWithError(self.resource_a)
+        self.assertAfterWithGeneratorInvariantsWithError(self.resource_b)
+
+    def testNestedExceptionBeforeInnerStatement(self):
+        mock_a = mock_contextmanager_generator()
+        mock_b = mock_contextmanager_generator()
+        self.bar = None
+        def shouldThrow():
+            with mock_a as self.foo:
+                self.assertInWithManagerInvariants(mock_a)
+                self.assertInWithGeneratorInvariants(self.foo)
+                self.raiseTestException()
+                with mock_b as self.bar:
+                    pass
+        self.assertRaises(RuntimeError, shouldThrow)
+        self.assertAfterWithManagerInvariantsWithError(mock_a)
+        self.assertAfterWithGeneratorInvariantsWithError(self.foo)
+
+        # The inner statement stuff should never have been touched
+        self.assertEqual(self.bar, None)
+        self.assertFalse(mock_b.context_called)
+        self.assertFalse(mock_b.enter_called)
+        self.assertFalse(mock_b.exit_called)
+        self.assertEqual(mock_b.exit_args, None)
+
+    def testNestedExceptionAfterInnerStatement(self):
+        mock_a = mock_contextmanager_generator()
+        mock_b = mock_contextmanager_generator()
+        def shouldThrow():
+            with mock_a as self.foo:
+                with mock_b as self.bar:
+                    self.assertInWithManagerInvariants(mock_a)
+                    self.assertInWithManagerInvariants(mock_b)
+                    self.assertInWithGeneratorInvariants(self.foo)
+                    self.assertInWithGeneratorInvariants(self.bar)
+                self.raiseTestException()
+        self.assertRaises(RuntimeError, shouldThrow)
+        self.assertAfterWithManagerInvariantsWithError(mock_a)
+        self.assertAfterWithManagerInvariantsNoError(mock_b)
+        self.assertAfterWithGeneratorInvariantsWithError(self.foo)
+        self.assertAfterWithGeneratorInvariantsNoError(self.bar)
+
+
+class NonLocalFlowControlTestCase(unittest.TestCase):
+
+    def testWithBreak(self):
+        counter = 0
+        while True:
+            counter += 1
+            with mock_contextmanager_generator():
+                counter += 10
+                break
+            counter += 100 # Not reached
+        self.assertEqual(counter, 11)
+
+    def testWithContinue(self):
+        counter = 0
+        while True:
+            counter += 1
+            if counter > 2:
+                break
+            with mock_contextmanager_generator():
+                counter += 10
+                continue
+            counter += 100 # Not reached
+        self.assertEqual(counter, 12)
+
+    def testWithReturn(self):
+        def foo():
+            counter = 0
+            while True:
+                counter += 1
+                with mock_contextmanager_generator():
+                    counter += 10
+                    return counter
+                counter += 100 # Not reached
+        self.assertEqual(foo(), 11)
+
+    def testWithYield(self):
+        def gen():
+            with mock_contextmanager_generator():
+                yield 12
+                yield 13
+        x = list(gen())
+        self.assertEqual(x, [12, 13])
+
+    def testWithRaise(self):
+        counter = 0
+        try:
+            counter += 1
+            with mock_contextmanager_generator():
+                counter += 10
+                raise RuntimeError
+            counter += 100 # Not reached
+        except RuntimeError:
+            self.assertEqual(counter, 11)
+        else:
+            self.fail("Didn't raise RuntimeError")
+
+
+class AssignmentTargetTestCase(unittest.TestCase):
+
+    def testSingleComplexTarget(self):
+        targets = {1: [0, 1, 2]}
+        with mock_contextmanager_generator() as targets[1][0]:
+            self.assertEqual(targets.keys(), [1])
+            self.assertEqual(targets[1][0].__class__, MockResource)
+        with mock_contextmanager_generator() as targets.values()[0][1]:
+            self.assertEqual(targets.keys(), [1])
+            self.assertEqual(targets[1][1].__class__, MockResource)
+        with mock_contextmanager_generator() as targets[2]:
+            keys = targets.keys()
+            keys.sort()
+            self.assertEqual(keys, [1, 2])
+        class C: pass
+        blah = C()
+        with mock_contextmanager_generator() as blah.foo:
+            self.assertEqual(hasattr(blah, "foo"), True)
+
+    def testMultipleComplexTargets(self):
+        class C:
+            def __context__(self): return self
+            def __enter__(self): return 1, 2, 3
+            def __exit__(self, *a): pass
+        targets = {1: [0, 1, 2]}
+        with C() as (targets[1][0], targets[1][1], targets[1][2]):
+            self.assertEqual(targets, {1: [1, 2, 3]})
+        with C() as (targets.values()[0][2], targets.values()[0][1], targets.values()[0][0]):
+            self.assertEqual(targets, {1: [3, 2, 1]})
+        with C() as (targets[1], targets[2], targets[3]):
+            self.assertEqual(targets, {1: 1, 2: 2, 3: 3})
+        class B: pass
+        blah = B()
+        with C() as (blah.one, blah.two, blah.three):
+            self.assertEqual(blah.one, 1)
+            self.assertEqual(blah.two, 2)
+            self.assertEqual(blah.three, 3)
+
+
+def test_main():
+    run_unittest(FailureTestCase, NonexceptionalTestCase,
+                 NestedNonexceptionalTestCase, ExceptionalTestCase,
+                 NonLocalFlowControlTestCase,
+                 AssignmentTargetTestCase)
+
+
+if __name__ == '__main__':
+    test_main()