diff --git a/Doc/library/dis.rst b/Doc/library/dis.rst index fb62ec14925..8e57dd48239 100644 --- a/Doc/library/dis.rst +++ b/Doc/library/dis.rst @@ -723,6 +723,12 @@ the more significant byte last. storage. +.. opcode:: DELETE_DEREF (i) + + Empties the cell contained in slot *i* of the cell and free variable storage. + Used by the :keyword:`del` statement. + + .. opcode:: SET_LINENO (lineno) This opcode is obsolete. diff --git a/Doc/reference/simple_stmts.rst b/Doc/reference/simple_stmts.rst index 378efc7a75a..4082aa70a3a 100644 --- a/Doc/reference/simple_stmts.rst +++ b/Doc/reference/simple_stmts.rst @@ -388,11 +388,6 @@ namespace, depending on whether the name occurs in a :keyword:`global` statement in the same code block. If the name is unbound, a :exc:`NameError` exception will be raised. -.. index:: pair: free; variable - -It is illegal to delete a name from the local namespace if it occurs as a free -variable in a nested block. - .. index:: pair: attribute; deletion Deletion of attribute references, subscriptions and slicings is passed to the @@ -400,6 +395,10 @@ primary object involved; deletion of a slicing is in general equivalent to assignment of an empty slice of the right type (but even this is determined by the sliced object). +.. versionchanged:: 3.2 + Previously it was illegal to delete a name from the local namespace if it + occurs as a free variable in a nested block. + .. _return: diff --git a/Doc/whatsnew/3.2.rst b/Doc/whatsnew/3.2.rst index 7d8970be843..bd38a7e123c 100644 --- a/Doc/whatsnew/3.2.rst +++ b/Doc/whatsnew/3.2.rst @@ -240,6 +240,31 @@ Some smaller changes made to the core Python language are: (See :issue:`8188`.) +* Previously it was illegal to delete a name from the local namespace if it + occurs as a free variable in a nested block:: + + >>> def outer(x): + ... def inner(): + ... return x + ... inner() + ... del x + + This is now allowed. Remember that the target of an :keyword:`except` clause + is cleared, so this code which used to work with Python 2.6, raised a + :exc:`SyntaxError` with Python 3.1 and now works again:: + + >>> def f(): + ... def print_error(): + ... print(e) + ... try: + ... something + ... except Exception as e: + ... print_error() + ... # implicit "del e" here + + (See :issue:`4617`.) + + New, Improved, and Deprecated Modules ===================================== diff --git a/Include/opcode.h b/Include/opcode.h index 1114c9386a8..6b1094449e9 100644 --- a/Include/opcode.h +++ b/Include/opcode.h @@ -123,6 +123,7 @@ extern "C" { #define LOAD_CLOSURE 135 /* Load free variable from closure */ #define LOAD_DEREF 136 /* Load and dereference from closure cell */ #define STORE_DEREF 137 /* Store into cell */ +#define DELETE_DEREF 138 /* Delete closure cell */ /* The next 3 opcodes must be contiguous and satisfy (CALL_FUNCTION_VAR - CALL_FUNCTION) & 3 == 1 */ diff --git a/Lib/opcode.py b/Lib/opcode.py index 9833b6ca64c..8e15d13e983 100644 --- a/Lib/opcode.py +++ b/Lib/opcode.py @@ -161,6 +161,8 @@ def_op('LOAD_DEREF', 136) hasfree.append(136) def_op('STORE_DEREF', 137) hasfree.append(137) +def_op('DELETE_DEREF', 138) +hasfree.append(138) def_op('CALL_FUNCTION_VAR', 140) # #args + (#kwargs << 8) def_op('CALL_FUNCTION_KW', 141) # #args + (#kwargs << 8) diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py index 126a57f5cef..e2824b27551 100644 --- a/Lib/test/test_exceptions.py +++ b/Lib/test/test_exceptions.py @@ -526,6 +526,17 @@ class ExceptionTests(unittest.TestCase): obj = wr() self.assertTrue(obj is None, "%s" % obj) + def test_exception_target_in_nested_scope(self): + # issue 4617: This used to raise a SyntaxError + # "can not delete variable 'e' referenced in nested scope" + def print_error(): + e + try: + something + except Exception as e: + print_error() + # implicit "del e" here + def test_generator_leaking(self): # Test that generator exception state doesn't leak into the calling # frame diff --git a/Lib/test/test_scope.py b/Lib/test/test_scope.py index 2ac34cf758e..0e5a8e92b42 100644 --- a/Lib/test/test_scope.py +++ b/Lib/test/test_scope.py @@ -217,13 +217,6 @@ class ScopeTests(unittest.TestCase): return f """) - check_syntax_error(self, """if 1: - def f(x): - def g(): - return x - del x # can't del name - """) - check_syntax_error(self, """if 1: def f(): def g(): @@ -272,6 +265,28 @@ class ScopeTests(unittest.TestCase): self.assertRaises(UnboundLocalError, errorInOuter) self.assertRaises(NameError, errorInInner) + def testUnboundLocal_AfterDel(self): + # #4617: It is now legal to delete a cell variable. + # The following functions must obviously compile, + # and give the correct error when accessing the deleted name. + def errorInOuter(): + y = 1 + del y + print(y) + def inner(): + return y + + def errorInInner(): + def inner(): + return y + y = 1 + del y + inner() + + self.assertRaises(UnboundLocalError, errorInOuter) + self.assertRaises(NameError, errorInInner) + + def testUnboundLocal_AugAssign(self): # test for bug #1501934: incorrect LOAD/STORE_GLOBAL generation exec("""if 1: global_x = 1 diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py index f354311ad0f..cd6b9a57f95 100644 --- a/Lib/test/test_syntax.py +++ b/Lib/test/test_syntax.py @@ -564,15 +564,6 @@ class SyntaxTestCase(unittest.TestCase): def test_break_outside_loop(self): self._check_error("break", "outside loop") - def test_delete_deref(self): - source = """if 1: - def foo(x): - def bar(): - print(x) - del x - """ - self._check_error(source, "nested scope") - def test_unexpected_indent(self): self._check_error("foo()\n bar()\n", "unexpected indent", subclass=IndentationError) diff --git a/Misc/NEWS b/Misc/NEWS index 6349b397ef7..11a14f2790d 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -10,6 +10,10 @@ What's New in Python 3.2 Alpha 3? Core and Builtins ----------------- +- Issue #4617: Previously it was illegal to delete a name from the local + namespace if it occurs as a free variable in a nested block. This limitation + of the compiler has been lifted, and a new opcode introduced (DELETE_DEREF). + - Issue #9804: ascii() now always represents unicode surrogate pairs as a single ``\UXXXXXXXX``, regardless of whether the character is printable or not. Also, the "backslashreplace" error handler now joins surrogate diff --git a/Python/ceval.c b/Python/ceval.c index 1f78f95b499..f0d278c5648 100644 --- a/Python/ceval.c +++ b/Python/ceval.c @@ -135,6 +135,7 @@ static PyObject * cmp_outcome(int, PyObject *, PyObject *); static PyObject * import_from(PyObject *, PyObject *); static int import_all_from(PyObject *, PyObject *); static void format_exc_check_arg(PyObject *, const char *, PyObject *); +static void format_exc_unbound(PyCodeObject *co, int oparg); static PyObject * unicode_concatenate(PyObject *, PyObject *, PyFrameObject *, unsigned char *); static PyObject * special_lookup(PyObject *, char *, PyObject **); @@ -2143,6 +2144,16 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag) ); break; + TARGET(DELETE_DEREF) + x = freevars[oparg]; + if (PyCell_GET(x) != NULL) { + PyCell_Set(x, NULL); + continue; + } + err = -1; + format_exc_unbound(co, oparg); + break; + TARGET(LOAD_CLOSURE) x = freevars[oparg]; Py_INCREF(x); @@ -2158,22 +2169,7 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag) DISPATCH(); } err = -1; - /* Don't stomp existing exception */ - if (PyErr_Occurred()) - break; - if (oparg < PyTuple_GET_SIZE(co->co_cellvars)) { - v = PyTuple_GET_ITEM(co->co_cellvars, - oparg); - format_exc_check_arg( - PyExc_UnboundLocalError, - UNBOUNDLOCAL_ERROR_MSG, - v); - } else { - v = PyTuple_GET_ITEM(co->co_freevars, oparg - - PyTuple_GET_SIZE(co->co_cellvars)); - format_exc_check_arg(PyExc_NameError, - UNBOUNDFREE_ERROR_MSG, v); - } + format_exc_unbound(co, oparg); break; TARGET(STORE_DEREF) @@ -4352,6 +4348,28 @@ format_exc_check_arg(PyObject *exc, const char *format_str, PyObject *obj) PyErr_Format(exc, format_str, obj_str); } +static void +format_exc_unbound(PyCodeObject *co, int oparg) +{ + PyObject *name; + /* Don't stomp existing exception */ + if (PyErr_Occurred()) + return; + if (oparg < PyTuple_GET_SIZE(co->co_cellvars)) { + name = PyTuple_GET_ITEM(co->co_cellvars, + oparg); + format_exc_check_arg( + PyExc_UnboundLocalError, + UNBOUNDLOCAL_ERROR_MSG, + name); + } else { + name = PyTuple_GET_ITEM(co->co_freevars, oparg - + PyTuple_GET_SIZE(co->co_cellvars)); + format_exc_check_arg(PyExc_NameError, + UNBOUNDFREE_ERROR_MSG, name); + } +} + static PyObject * unicode_concatenate(PyObject *v, PyObject *w, PyFrameObject *f, unsigned char *next_instr) diff --git a/Python/compile.c b/Python/compile.c index 6963a151a76..5341e6b5359 100644 --- a/Python/compile.c +++ b/Python/compile.c @@ -857,6 +857,8 @@ opcode_stack_effect(int opcode, int oparg) return 1; case STORE_DEREF: return -1; + case DELETE_DEREF: + return 0; default: fprintf(stderr, "opcode = %d\n", opcode); Py_FatalError("opcode_stack_effect()"); @@ -2506,13 +2508,7 @@ compiler_nameop(struct compiler *c, identifier name, expr_context_ty ctx) case AugLoad: case AugStore: break; - case Del: - PyErr_Format(PyExc_SyntaxError, - "can not delete variable '%S' referenced " - "in nested scope", - name); - Py_DECREF(mangled); - return 0; + case Del: op = DELETE_DEREF; break; case Param: default: PyErr_SetString(PyExc_SystemError, diff --git a/Python/opcode_targets.h b/Python/opcode_targets.h index 8b59c2db788..a91da79be69 100644 --- a/Python/opcode_targets.h +++ b/Python/opcode_targets.h @@ -137,7 +137,7 @@ static void *opcode_targets[256] = { &&TARGET_LOAD_CLOSURE, &&TARGET_LOAD_DEREF, &&TARGET_STORE_DEREF, - &&_unknown_opcode, + &&TARGET_DELETE_DEREF, &&_unknown_opcode, &&TARGET_CALL_FUNCTION_VAR, &&TARGET_CALL_FUNCTION_KW,