[Python-checkins] r72924 - in python/trunk: Doc/reference/compound_stmts.rst Grammar/Grammar Include/graminit.h Lib/compiler/transformer.py Lib/test/test_compiler.py Lib/test/test_parser.py Lib/test/test_with.py Misc/NEWS Modules/parsermodule.c Python/ast.c Python/graminit.c

Mon May 25 23:02:56 CEST 2009

Author: georg.brandl
Date: Mon May 25 23:02:56 2009
New Revision: 72924
Log:
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.
Modified:
 python/trunk/Doc/reference/compound_stmts.rst
 python/trunk/Grammar/Grammar
 python/trunk/Include/graminit.h
 python/trunk/Lib/compiler/transformer.py
 python/trunk/Lib/test/test_compiler.py
 python/trunk/Lib/test/test_parser.py
 python/trunk/Lib/test/test_with.py
 python/trunk/Misc/NEWS
 python/trunk/Modules/parsermodule.c
 python/trunk/Python/ast.c
 python/trunk/Python/graminit.c
Modified: python/trunk/Doc/reference/compound_stmts.rst
==============================================================================

--- python/trunk/Doc/reference/compound_stmts.rst	(original)
+++ python/trunk/Doc/reference/compound_stmts.rst	Mon May 25 23:02:56 2009
@@ -333,9 +333,10 @@
 patterns to be encapsulated for convenient reuse.
 
 .. productionlist::
- with_stmt: "with" `expression` ["as" `target`] ":" `suite`
+ with_stmt: "with" with_item ("," with_item)* ":" `suite`
+ with_item: `expression` ["as" `target`]
 
-The execution of the :keyword:`with` statement proceeds as follows:
+The execution of the :keyword:`with` statement with one "item" proceeds as follows:
 
 #. The context expression is evaluated to obtain a context manager.
 
@@ -369,12 +370,27 @@
 from :meth:`__exit__` is ignored, and execution proceeds at the normal location
 for the kind of exit that was taken.
 
+With more than one item, the context managers are processed as if multiple
+:keyword:`with` statements were nested::
+
+ with A() as a, B() as b:
+ suite
+
+is equivalent to ::
+
+ with A() as a:
+ with B() as b:
+ suite
+
 .. note::
 
 In Python 2.5, the :keyword:`with` statement is only allowed when the
 ``with_statement`` feature has been enabled. It is always enabled in
 Python 2.6.
 
+.. versionchanged:: 2.7
+ Support for multiple context expressions.
+
 .. seealso::
 
 :pep:`0343` - The "with" statement
Modified: python/trunk/Grammar/Grammar
==============================================================================
--- python/trunk/Grammar/Grammar	(original)
+++ python/trunk/Grammar/Grammar	Mon May 25 23:02:56 2009
@@ -83,8 +83,8 @@
 	 ['else' ':' suite]
 	 ['finally' ':' suite] |
 	 'finally' ':' suite))
-with_stmt: 'with' test [ with_var ] ':' suite
-with_var: 'as' expr
+with_stmt: 'with' with_item (',' with_item)* ':' suite
+with_item: test ['as' expr]
 # NB compile.c makes sure that the default except clause is last
 except_clause: 'except' [test [('as' | ',') test]]
 suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT
Modified: python/trunk/Include/graminit.h
==============================================================================
--- python/trunk/Include/graminit.h	(original)
+++ python/trunk/Include/graminit.h	Mon May 25 23:02:56 2009
@@ -42,7 +42,7 @@
 #define for_stmt 295
 #define try_stmt 296
 #define with_stmt 297
-#define with_var 298
+#define with_item 298
 #define except_clause 299
 #define suite 300
 #define testlist_safe 301
Modified: python/trunk/Lib/compiler/transformer.py
==============================================================================
--- python/trunk/Lib/compiler/transformer.py	(original)
+++ python/trunk/Lib/compiler/transformer.py	Mon May 25 23:02:56 2009
@@ -965,18 +965,22 @@
 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
Modified: python/trunk/Lib/test/test_compiler.py
==============================================================================
--- python/trunk/Lib/test/test_compiler.py	(original)
+++ python/trunk/Lib/test/test_compiler.py	Mon May 25 23:02:56 2009
@@ -165,6 +165,27 @@
 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__': {}}
Modified: python/trunk/Lib/test/test_parser.py
==============================================================================
--- python/trunk/Lib/test/test_parser.py	(original)
+++ python/trunk/Lib/test/test_parser.py	Mon May 25 23:02:56 2009
@@ -199,6 +199,7 @@
 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")
Modified: python/trunk/Lib/test/test_with.py
==============================================================================
--- python/trunk/Lib/test/test_with.py	(original)
+++ python/trunk/Lib/test/test_with.py	Mon May 25 23:02:56 2009
@@ -654,12 +654,88 @@
 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__':
Modified: python/trunk/Misc/NEWS
==============================================================================
--- python/trunk/Misc/NEWS	(original)
+++ python/trunk/Misc/NEWS	Mon May 25 23:02:56 2009
@@ -12,6 +12,8 @@
 Core and Builtins
 -----------------
 
+- Added support for multiple context managers in the same with statement.
+
 - Issue #6101: A new opcode, SETUP_WITH, has been added to speed up the with
 statement and correctly lookup the __enter__ and __exit__ special methods.
 
Modified: python/trunk/Modules/parsermodule.c
==============================================================================
--- python/trunk/Modules/parsermodule.c	(original)
+++ python/trunk/Modules/parsermodule.c	Mon May 25 23:02:56 2009
@@ -2618,36 +2618,39 @@
 return ok;
 }
 
-/* with_var
-with_var: 'as' expr
+/* with_item:
+ * test ['as' expr]
 */
 static int
-validate_with_var(node *tree)
+validate_with_item(node *tree)
 {
 int nch = NCH(tree);
- int ok = (validate_ntype(tree, with_var)
- && (nch == 2)
- && validate_name(CHILD(tree, 0), "as")
- && validate_expr(CHILD(tree, 1)));
- return ok;
+ int ok = (validate_ntype(tree, with_item)
+ && (nch == 1 || nch == 3)
+ && validate_test(CHILD(tree, 0)));
+ if (ok && nch == 3) 
+ ok = (validate_name(CHILD(tree, 1), "as")
+ && validate_expr(CHILD(tree, 2)));
+ return ok;
 }
 
-/* with_stmt
- * 0 1 2 -2 -1
-with_stmt: 'with' test [ with_var ] ':' suite
+/* with_stmt:
+ * 0 1 ... -2 -1
+ * 'with' with_item (',' with_item)* ':' suite
 */
 static int
 validate_with_stmt(node *tree)
 {
+ int i;
 int nch = NCH(tree);
 int ok = (validate_ntype(tree, with_stmt)
- && ((nch == 4) || (nch == 5))
+ && (nch % 2 == 0)
 && validate_name(CHILD(tree, 0), "with")
- && validate_test(CHILD(tree, 1))
- && (nch == 4 || validate_with_var(CHILD(tree, 2))) 
 && validate_colon(RCHILD(tree, -2))
 && validate_suite(RCHILD(tree, -1)));
- return ok;
+ for (i = 1; ok && i < nch - 2; i += 2)
+ ok = validate_with_item(CHILD(tree, i));
+ return ok;
 }
 
 /* funcdef:
Modified: python/trunk/Python/ast.c
==============================================================================
--- python/trunk/Python/ast.c	(original)
+++ python/trunk/Python/ast.c	Mon May 25 23:02:56 2009
@@ -3009,27 +3009,18 @@
 return TryFinally(body, finally, LINENO(n), n->n_col_offset, c->c_arena);
 }
 
-static expr_ty
-ast_for_with_var(struct compiling *c, const node *n)
-{
- REQ(n, with_var);
- return ast_for_expr(c, CHILD(n, 1));
-}
-
-/* with_stmt: 'with' test [ with_var ] ':' suite */
+/* with_item: test ['as' expr] */
 static stmt_ty
-ast_for_with_stmt(struct compiling *c, const node *n)
+ast_for_with_item(struct compiling *c, const node *n, asdl_seq *content)
 {
 expr_ty context_expr, optional_vars = NULL;
- int suite_index = 3; /* skip 'with', test, and ':' */
- asdl_seq *suite_seq;
 
- assert(TYPE(n) == with_stmt);
- context_expr = ast_for_expr(c, CHILD(n, 1));
+ REQ(n, with_item);
+ context_expr = ast_for_expr(c, CHILD(n, 0));
 if (!context_expr)
 return NULL;
- if (TYPE(CHILD(n, 2)) == with_var) {
- optional_vars = ast_for_with_var(c, CHILD(n, 2));
+ if (NCH(n) == 3) {
+ optional_vars = ast_for_expr(c, CHILD(n, 2));
 
 if (!optional_vars) {
 return NULL;
@@ -3037,15 +3028,45 @@
 if (!set_context(c, optional_vars, Store, n)) {
 return NULL;
 }
- suite_index = 4;
 }
 
- suite_seq = ast_for_suite(c, CHILD(n, suite_index));
- if (!suite_seq) {
+ return With(context_expr, optional_vars, content, LINENO(n),
+ n->n_col_offset, c->c_arena);
+}
+
+/* with_stmt: 'with' with_item (',' with_item)* ':' suite */
+static stmt_ty
+ast_for_with_stmt(struct compiling *c, const node *n)
+{
+ int i;
+ stmt_ty ret;
+ asdl_seq *inner;
+
+ REQ(n, with_stmt);
+
+ /* process the with items inside-out */
+ i = NCH(n) - 1;
+ /* the suite of the innermost with item is the suite of the with stmt */
+ inner = ast_for_suite(c, CHILD(n, i));
+ if (!inner)
 return NULL;
+
+ for (;;) {
+ i -= 2;
+ ret = ast_for_with_item(c, CHILD(n, i), inner);
+ if (!ret)
+ return NULL;
+ /* was this the last item? */
+ if (i == 1)
+ break;
+ /* if not, wrap the result so far in a new sequence */
+ inner = asdl_seq_new(1, c->c_arena);
+ if (!inner)
+ return NULL;
+ asdl_seq_SET(inner, 0, ret);
 }
- return With(context_expr, optional_vars, suite_seq, LINENO(n), 
- n->n_col_offset, c->c_arena);
+
+ return ret;
 }
 
 static stmt_ty
Modified: python/trunk/Python/graminit.c
==============================================================================
--- python/trunk/Python/graminit.c	(original)
+++ python/trunk/Python/graminit.c	Mon May 25 23:02:56 2009
@@ -901,42 +901,43 @@
 	{100, 1},
 };
 static arc arcs_41_1[1] = {
-	{28, 2},
+	{101, 2},
 };
 static arc arcs_41_2[2] = {
-	{101, 3},
-	{23, 4},
+	{29, 1},
+	{23, 3},
 };
 static arc arcs_41_3[1] = {
-	{23, 4},
+	{24, 4},
 };
 static arc arcs_41_4[1] = {
-	{24, 5},
-};
-static arc arcs_41_5[1] = {
-	{0, 5},
+	{0, 4},
 };
-static state states_41[6] = {
+static state states_41[5] = {
 	{1, arcs_41_0},
 	{1, arcs_41_1},
 	{2, arcs_41_2},
 	{1, arcs_41_3},
 	{1, arcs_41_4},
-	{1, arcs_41_5},
 };
 static arc arcs_42_0[1] = {
-	{80, 1},
+	{28, 1},
 };
-static arc arcs_42_1[1] = {
-	{84, 2},
+static arc arcs_42_1[2] = {
+	{80, 2},
+	{0, 1},
 };
 static arc arcs_42_2[1] = {
-	{0, 2},
+	{84, 3},
 };
-static state states_42[3] = {
+static arc arcs_42_3[1] = {
+	{0, 3},
+};
+static state states_42[4] = {
 	{1, arcs_42_0},
-	{1, arcs_42_1},
+	{2, arcs_42_1},
 	{1, arcs_42_2},
+	{1, arcs_42_3},
 };
 static arc arcs_43_0[1] = {
 	{102, 1},
@@ -1877,10 +1878,10 @@
 	 "000円000円000円000円000円000円000円000円000円000円000円000円001円000円000円000円000円000円000円000円000円000円"},
 	{296, "try_stmt", 0, 13, states_40,
 	 "000円000円000円000円000円000円000円000円000円000円000円000円002円000円000円000円000円000円000円000円000円000円"},
-	{297, "with_stmt", 0, 6, states_41,
+	{297, "with_stmt", 0, 5, states_41,
 	 "000円000円000円000円000円000円000円000円000円000円000円000円020円000円000円000円000円000円000円000円000円000円"},
-	{298, "with_var", 0, 3, states_42,
-	 "000円000円000円000円000円000円000円000円000円000円001円000円000円000円000円000円000円000円000円000円000円000円"},
+	{298, "with_item", 0, 4, states_42,
+	 "000円040円040円000円000円000円000円000円000円000円000円000円000円040円010円000円200円041円044円015円000円000円"},
 	{299, "except_clause", 0, 5, states_43,
 	 "000円000円000円000円000円000円000円000円000円000円000円000円100円000円000円000円000円000円000円000円000円000円"},
 	{300, "suite", 0, 5, states_44,
