[Python-checkins] cpython: PEP 415: Implement suppression of __context__ display with an exception

benjamin.peterson python-checkins at python.org
Tue May 15 07:09:55 CEST 2012

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http://hg.python.org/cpython/rev/b0eb7d2a9542
changeset: 76942:b0eb7d2a9542
parent: 76939:6ff172db8114
user: Benjamin Peterson <benjamin at python.org>
date: Mon May 14 22:09:31 2012 -0700
summary:
 PEP 415: Implement suppression of __context__ display with an exception attribute
This replaces the original PEP 409 implementation. See #14133.
files:
 Doc/c-api/exceptions.rst | 8 +----
 Doc/library/exceptions.rst | 21 ++++++------
 Doc/library/stdtypes.rst | 9 ++---
 Include/pyerrors.h | 4 +-
 Lib/test/test_exceptions.py | 15 ++++----
 Lib/test/test_raise.py | 7 +++-
 Lib/test/test_sys.py | 6 +-
 Lib/traceback.py | 13 ++++---
 Misc/NEWS | 3 +
 Objects/exceptions.c | 41 ++++++++++++------------
 Python/ceval.c | 21 +++++++-----
 Python/pythonrun.c | 9 +---
 12 files changed, 79 insertions(+), 78 deletions(-)
diff --git a/Doc/c-api/exceptions.rst b/Doc/c-api/exceptions.rst
--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -471,10 +471,6 @@
 set by ``raise ... from ...``) associated with the exception as a new
 reference, as accessible from Python through :attr:`__cause__`.
 
- If there is no cause associated, this returns *NULL* (from Python
- ``__cause__ is Ellipsis``). If the cause is :const:`None`, the default
- exception display routines stop showing the context chain.
-
 
 .. c:function:: void PyException_SetCause(PyObject *ex, PyObject *ctx)
 
@@ -482,9 +478,7 @@
 it. There is no type check to make sure that *ctx* is either an exception
 instance or :const:`None`. This steals a reference to *ctx*.
 
- If the cause is set to :const:`None` the default exception display
- routines will not display this exception's context, and will not follow the
- chain any further.
+ :attr:`__suppress_context__` is implicitly set to ``True`` by this function.
 
 
 .. _unicodeexceptions:
diff --git a/Doc/library/exceptions.rst b/Doc/library/exceptions.rst
--- a/Doc/library/exceptions.rst
+++ b/Doc/library/exceptions.rst
@@ -39,18 +39,17 @@
 new exception is not handled the traceback that is eventually displayed will
 include the originating exception(s) and the final exception.
 
-This implicit exception chain can be made explicit by using :keyword:`from`
-with :keyword:`raise`. The single argument to :keyword:`from` must be an
-exception or :const:`None`, and it will be set as :attr:`__cause__` on the
-raised exception. If :attr:`__cause__` is an exception it will be displayed
-instead of :attr:`__context__`; if :attr:`__cause__` is None,
-:attr:`__context__` will not be displayed by the default exception handling
-code. (Note: the default value for :attr:`__context__` is :const:`None`,
-while the default value for :attr:`__cause__` is :const:`Ellipsis`.)
+This implicit exception chain can be made explicit by using :keyword:`from` with
+:keyword:`raise`. The single argument to :keyword:`from` must be an exception
+or ``None``. It will be set as :attr:`__cause__` on the raised exception.
+Setting :attr:`__cause__` implicitly sets the :attr:`__suppress_context__` to
+``True``. If :attr:`__cause__` is an exception, it will be displayed. If
+:attr:`__cause__` is present or :attr:`__suppress_context__` has a true value,
+:attr:`__context__` will not be displayed.
 
-In either case, the default exception handling code will not display
-any of the remaining links in the :attr:`__context__` chain if
-:attr:`__cause__` has been set.
+In either case, the default exception handling code will not display any of the
+remaining links in the :attr:`__context__` chain if :attr:`__cause__` has been
+set.
 
 
 Base classes
diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -2996,11 +2996,10 @@
 The Ellipsis Object
 -------------------
 
-This object is commonly used by slicing (see :ref:`slicings`), but may also
-be used in other situations where a sentinel value other than :const:`None`
-is needed. It supports no special operations. There is exactly one ellipsis
-object, named :const:`Ellipsis` (a built-in name). ``type(Ellipsis)()``
-produces the :const:`Ellipsis` singleton.
+This object is commonly used by slicing (see :ref:`slicings`). It supports no
+special operations. There is exactly one ellipsis object, named
+:const:`Ellipsis` (a built-in name). ``type(Ellipsis)()`` produces the
+:const:`Ellipsis` singleton.
 
 It is written as ``Ellipsis`` or ``...``.
 
diff --git a/Include/pyerrors.h b/Include/pyerrors.h
--- a/Include/pyerrors.h
+++ b/Include/pyerrors.h
@@ -10,7 +10,8 @@
 /* PyException_HEAD defines the initial segment of every exception class. */
 #define PyException_HEAD PyObject_HEAD PyObject *dict;\
 PyObject *args; PyObject *traceback;\
- PyObject *context; PyObject *cause;
+ PyObject *context; PyObject *cause;\
+ int suppress_context;
 
 typedef struct {
 PyException_HEAD
@@ -114,7 +115,6 @@
 /* Cause manipulation (PEP 3134) */
 PyAPI_FUNC(PyObject *) PyException_GetCause(PyObject *);
 PyAPI_FUNC(void) PyException_SetCause(PyObject *, PyObject *);
-PyAPI_FUNC(int) _PyException_SetCauseChecked(PyObject *, PyObject *);
 
 /* Context manipulation (PEP 3134) */
 PyAPI_FUNC(PyObject *) PyException_GetContext(PyObject *);
diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -388,18 +388,18 @@
 def testChainingAttrs(self):
 e = Exception()
 self.assertIsNone(e.__context__)
- self.assertIs(e.__cause__, Ellipsis)
+ self.assertIsNone(e.__cause__)
 
 e = TypeError()
 self.assertIsNone(e.__context__)
- self.assertIs(e.__cause__, Ellipsis)
+ self.assertIsNone(e.__cause__)
 
 class MyException(EnvironmentError):
 pass
 
 e = MyException()
 self.assertIsNone(e.__context__)
- self.assertIs(e.__cause__, Ellipsis)
+ self.assertIsNone(e.__cause__)
 
 def testChainingDescriptors(self):
 try:
@@ -408,15 +408,16 @@
 e = exc
 
 self.assertIsNone(e.__context__)
- self.assertIs(e.__cause__, Ellipsis)
+ self.assertIsNone(e.__cause__)
+ self.assertFalse(e.__suppress_context__)
 
 e.__context__ = NameError()
 e.__cause__ = None
 self.assertIsInstance(e.__context__, NameError)
 self.assertIsNone(e.__cause__)
-
- e.__cause__ = Ellipsis
- self.assertIs(e.__cause__, Ellipsis)
+ self.assertTrue(e.__suppress_context__)
+ e.__suppress_context__ = False
+ self.assertFalse(e.__suppress_context__)
 
 def testKeywordArgs(self):
 # test that builtin exception don't take keyword args,
diff --git a/Lib/test/test_raise.py b/Lib/test/test_raise.py
--- a/Lib/test/test_raise.py
+++ b/Lib/test/test_raise.py
@@ -174,11 +174,14 @@
 raise ValueError from None
 except ValueError as exc:
 self.assertIsNone(exc.__cause__)
- raise exc from Ellipsis
+ self.assertTrue(exc.__suppress_context__)
+ exc.__suppress_context__ = False
+ raise exc
 except ValueError as exc:
 e = exc
 
- self.assertIs(e.__cause__, Ellipsis)
+ self.assertIsNone(e.__cause__)
+ self.assertFalse(e.__suppress_context__)
 self.assertIsInstance(e.__context__, TypeError)
 
 def test_invalid_cause(self):
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -700,14 +700,14 @@
 class C(object): pass
 check(C.__dict__, size(h + 'P'))
 # BaseException
- check(BaseException(), size(h + '5P'))
+ check(BaseException(), size(h + '5Pi'))
 # UnicodeEncodeError
- check(UnicodeEncodeError("", "", 0, 0, ""), size(h + '5P 2P2PP'))
+ check(UnicodeEncodeError("", "", 0, 0, ""), size(h + '5Pi 2P2PP'))
 # UnicodeDecodeError
 # XXX
 # check(UnicodeDecodeError("", "", 0, 0, ""), size(h + '5P2PP'))
 # UnicodeTranslateError
- check(UnicodeTranslateError("", 0, 1, ""), size(h + '5P 2P2PP'))
+ check(UnicodeTranslateError("", 0, 1, ""), size(h + '5Pi 2P2PP'))
 # ellipses
 check(Ellipsis, size(h + ''))
 # EncodingMap
diff --git a/Lib/traceback.py b/Lib/traceback.py
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -119,15 +119,16 @@
 seen = set()
 seen.add(exc)
 its = []
+ context = exc.__context__
 cause = exc.__cause__
- if cause is Ellipsis:
- context = exc.__context__
- if context is not None and context not in seen:
- its.append(_iter_chain(context, None, seen))
- its.append([(_context_message, None)])
- elif cause is not None and cause not in seen:
+ if cause is not None and cause not in seen:
 its.append(_iter_chain(cause, False, seen))
 its.append([(_cause_message, None)])
+ elif (context is not None and
+ not exc.__suppress_context__ and
+ context not in seen):
+ its.append(_iter_chain(context, None, seen))
+ its.append([(_context_message, None)])
 its.append([(exc, custom_tb or exc.__traceback__)])
 # itertools.chain is in an extension module and may be unavailable
 for it in its:
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@
 Core and Builtins
 -----------------
 
+- Issue #14133 (PEP 415): Implement suppression of __context__ display with an
+ attribute on BaseException. This replaces the original mechanism of PEP 409.
+
 - Issue #14417: Mutating a dict during lookup now restarts the lookup instead
 of raising a RuntimeError (undoes issue #14205).
 
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -42,6 +42,7 @@
 /* the dict is created on the fly in PyObject_GenericSetAttr */
 self->dict = NULL;
 self->traceback = self->cause = self->context = NULL;
+ self->suppress_context = 0;
 
 self->args = PyTuple_New(0);
 if (!self->args) {
@@ -266,24 +267,7 @@
 PyObject *res = PyException_GetCause(self);
 if (res)
 return res; /* new reference already returned above */
- Py_INCREF(Py_Ellipsis);
- return Py_Ellipsis;
-}
-
-int
-_PyException_SetCauseChecked(PyObject *self, PyObject *arg) {
- if (arg == Py_Ellipsis) {
- arg = NULL;
- } else if (arg != Py_None && !PyExceptionInstance_Check(arg)) {
- PyErr_SetString(PyExc_TypeError, "exception cause must be None, "
- "Ellipsis or derive from BaseException");
- return -1;
- } else {
- /* PyException_SetCause steals a reference */
- Py_INCREF(arg);
- }
- PyException_SetCause(self, arg);
- return 0;
+ Py_RETURN_NONE;
 }
 
 static int
@@ -291,8 +275,18 @@
 if (arg == NULL) {
 PyErr_SetString(PyExc_TypeError, "__cause__ may not be deleted");
 return -1;
+ } else if (arg == Py_None) {
+ arg = NULL;
+ } else if (!PyExceptionInstance_Check(arg)) {
+ PyErr_SetString(PyExc_TypeError, "exception cause must be None "
+ "or derive from BaseException");
+ return -1;
+ } else {
+ /* PyException_SetCause steals this reference */
+ Py_INCREF(arg);
 }
- return _PyException_SetCauseChecked(self, arg);
+ PyException_SetCause(self, arg);
+ return 0;
 }
 
 
@@ -333,6 +327,7 @@
 PyException_SetCause(PyObject *self, PyObject *cause) {
 PyObject *old_cause = ((PyBaseExceptionObject *)self)->cause;
 ((PyBaseExceptionObject *)self)->cause = cause;
+ ((PyBaseExceptionObject *)self)->suppress_context = 1;
 Py_XDECREF(old_cause);
 }
 
@@ -352,6 +347,12 @@
 }
 
 
+static struct PyMemberDef BaseException_members[] = {
+ {"__suppress_context__", T_BOOL,
+ offsetof(PyBaseExceptionObject, suppress_context)}
+};
+
+
 static PyTypeObject _PyExc_BaseException = {
 PyVarObject_HEAD_INIT(NULL, 0)
 "BaseException", /*tp_name*/
@@ -382,7 +383,7 @@
 0, /* tp_iter */
 0, /* tp_iternext */
 BaseException_methods, /* tp_methods */
- 0, /* tp_members */
+ BaseException_members, /* tp_members */
 BaseException_getset, /* tp_getset */
 0, /* tp_base */
 0, /* tp_dict */
diff --git a/Python/ceval.c b/Python/ceval.c
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -3572,23 +3572,26 @@
 
 if (cause) {
 PyObject *fixed_cause;
- int result;
 if (PyExceptionClass_Check(cause)) {
 fixed_cause = PyObject_CallObject(cause, NULL);
 if (fixed_cause == NULL)
 goto raise_error;
- Py_CLEAR(cause);
- } else {
- /* Let "exc.__cause__ = cause" handle all further checks */
+ Py_DECREF(cause);
+ }
+ else if (PyExceptionInstance_Check(cause)) {
 fixed_cause = cause;
- cause = NULL; /* Steal the reference */
 }
- /* We retain ownership of the reference to fixed_cause */
- result = _PyException_SetCauseChecked(value, fixed_cause);
- Py_DECREF(fixed_cause);
- if (result < 0) {
+ else if (cause == Py_None) {
+ Py_DECREF(cause);
+ fixed_cause = NULL;
+ }
+ else {
+ PyErr_SetString(PyExc_TypeError,
+ "exception causes must derive from "
+ "BaseException");
 goto raise_error;
 }
+ PyException_SetCause(value, fixed_cause);
 }
 
 PyErr_SetObject(type, value);
diff --git a/Python/pythonrun.c b/Python/pythonrun.c
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -1761,11 +1761,7 @@
 else if (PyExceptionInstance_Check(value)) {
 cause = PyException_GetCause(value);
 context = PyException_GetContext(value);
- if (cause && cause == Py_None) {
- /* print neither cause nor context */
- ;
- }
- else if (cause) {
+ if (cause) {
 res = PySet_Contains(seen, cause);
 if (res == -1)
 PyErr_Clear();
@@ -1776,7 +1772,8 @@
 cause_message, f);
 }
 }
- else if (context) {
+ else if (context &&
+ !((PyBaseExceptionObject *)value)->suppress_context) {
 res = PySet_Contains(seen, context);
 if (res == -1)
 PyErr_Clear();
-- 
Repository URL: http://hg.python.org/cpython

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