Allow multiple context managers in one with statement, as proposed

in http://codereview.appspot.com/53094 and accepted by Guido.

The construct is transformed into multiple With AST nodes so that
there should be no problems with the semantics.

4 files changed, 113 insertions, 11 deletions

diff --git a/Lib/compiler/transformer.py b/Lib/compiler/transformer.py
index f5fe582..2a156d3 100644
--- a/Lib/compiler/transformer.py
+++ b/Lib/compiler/transformer.py
@@ -965,18 +965,22 @@ class Transformer:
             return try_except
 
     def com_with(self, nodelist):
-        # with_stmt: 'with' expr [with_var] ':' suite
-        expr = self.com_node(nodelist[1])
+        # with_stmt: 'with' with_item (',' with_item)* ':' suite
         body = self.com_node(nodelist[-1])
-        if nodelist[2][0] == token.COLON:
-            var = None
+        for i in range(len(nodelist) - 3, 0, -2):
+            ret = self.com_with_item(nodelist[i], body, nodelist[0][2])
+            if i == 1:
+                return ret
+            body = ret
+
+    def com_with_item(self, nodelist, body, lineno):
+        # with_item: test ['as' expr]
+        if len(nodelist) == 4:
+            var = self.com_assign(nodelist[3], OP_ASSIGN)
         else:
-            var = self.com_assign(nodelist[2][2], OP_ASSIGN)
-        return With(expr, var, body, lineno=nodelist[0][2])
-
-    def com_with_var(self, nodelist):
-        # with_var: 'as' expr
-        return self.com_node(nodelist[1])
+            var = None
+        expr = self.com_node(nodelist[1])
+        return With(expr, var, body, lineno=lineno)
 
     def com_augassign_op(self, node):
         assert node[0] == symbol.augassign
diff --git a/Lib/test/test_compiler.py b/Lib/test/test_compiler.py
index 052e07e..f1fef74 100644
--- a/Lib/test/test_compiler.py
+++ b/Lib/test/test_compiler.py
@@ -165,6 +165,27 @@ class CompilerTest(unittest.TestCase):
         exec c in dct
         self.assertEquals(dct.get('result'), 1)
 
+    def testWithMult(self):
+        events = []
+        class Ctx:
+            def __init__(self, n):
+                self.n = n
+            def __enter__(self):
+                events.append(self.n)
+            def __exit__(self, *args):
+                pass
+        c = compiler.compile('from __future__ import with_statement\n'
+                             'def f():\n'
+                             '    with Ctx(1) as tc, Ctx(2) as tc2:\n'
+                             '        return 1\n'
+                             'result = f()',
+                             '<string>',
+                             'exec' )
+        dct = {'Ctx': Ctx}
+        exec c in dct
+        self.assertEquals(dct.get('result'), 1)
+        self.assertEquals(events, [1, 2])
+
     def testGlobal(self):
         code = compiler.compile('global x\nx=1', '<string>', 'exec')
         d1 = {'__builtins__': {}}
diff --git a/Lib/test/test_parser.py b/Lib/test/test_parser.py
index 23f418e..7d059c2 100644
--- a/Lib/test/test_parser.py
+++ b/Lib/test/test_parser.py
@@ -199,6 +199,7 @@ class RoundtripLegalSyntaxTestCase(unittest.TestCase):
     def test_with(self):
         self.check_suite("with open('x'): pass\n")
         self.check_suite("with open('x') as f: pass\n")
+        self.check_suite("with open('x') as f, open('y') as g: pass\n")
 
     def test_try_stmt(self):
         self.check_suite("try: pass\nexcept: pass\n")
diff --git a/Lib/test/test_with.py b/Lib/test/test_with.py
index bfeb06b..68ae890 100644
--- a/Lib/test/test_with.py
+++ b/Lib/test/test_with.py
@@ -654,12 +654,88 @@ class ExitSwallowsExceptionTestCase(unittest.TestCase):
             self.fail("ZeroDivisionError should have been raised")
 
 
+class NestedWith(unittest.TestCase):
+
+    class Dummy(object):
+        def __init__(self, value=None, gobble=False):
+            if value is None:
+                value = self
+            self.value = value
+            self.gobble = gobble
+            self.enter_called = False
+            self.exit_called = False
+
+        def __enter__(self):
+            self.enter_called = True
+            return self.value
+
+        def __exit__(self, *exc_info):
+            self.exit_called = True
+            self.exc_info = exc_info
+            if self.gobble:
+                return True
+
+    class CtorRaises(object):
+        def __init__(self): raise RuntimeError()
+
+    class EnterRaises(object):
+        def __enter__(self): raise RuntimeError()
+        def __exit__(self, *exc_info): pass
+
+    class ExitRaises(object):
+        def __enter__(self): pass
+        def __exit__(self, *exc_info): raise RuntimeError()
+
+    def testNoExceptions(self):
+        with self.Dummy() as a, self.Dummy() as b:
+            self.assertTrue(a.enter_called)
+            self.assertTrue(b.enter_called)
+        self.assertTrue(a.exit_called)
+        self.assertTrue(b.exit_called)
+
+    def testExceptionInExprList(self):
+        try:
+            with self.Dummy() as a, self.CtorRaises():
+                pass
+        except:
+            pass
+        self.assertTrue(a.enter_called)
+        self.assertTrue(a.exit_called)
+
+    def testExceptionInEnter(self):
+        try:
+            with self.Dummy() as a, self.EnterRaises():
+                self.fail('body of bad with executed')
+        except RuntimeError:
+            pass
+        else:
+            self.fail('RuntimeError not reraised')
+        self.assertTrue(a.enter_called)
+        self.assertTrue(a.exit_called)
+
+    def testExceptionInExit(self):
+        body_executed = False
+        with self.Dummy(gobble=True) as a, self.ExitRaises():
+            body_executed = True
+        self.assertTrue(a.enter_called)
+        self.assertTrue(a.exit_called)
+        self.assertNotEqual(a.exc_info[0], None)
+
+    def testEnterReturnsTuple(self):
+        with self.Dummy(value=(1,2)) as (a1, a2), \
+             self.Dummy(value=(10, 20)) as (b1, b2):
+            self.assertEquals(1, a1)
+            self.assertEquals(2, a2)
+            self.assertEquals(10, b1)
+            self.assertEquals(20, b2)
+
 def test_main():
     run_unittest(FailureTestCase, NonexceptionalTestCase,
                  NestedNonexceptionalTestCase, ExceptionalTestCase,
                  NonLocalFlowControlTestCase,
                  AssignmentTargetTestCase,
-                 ExitSwallowsExceptionTestCase)
+                 ExitSwallowsExceptionTestCase,
+                 NestedWith)
 
 
 if __name__ == '__main__':