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#3021: Antoine Pitrou's Lexical exception handlers

This commit is contained in:
Benjamin Peterson 2008-06-11 15:59:43 +00:00
parent e8465f2b41
commit eec3d71379
17 changed files with 410 additions and 303 deletions
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36
Doc/library/dis.rst
View File

@ -397,6 +397,14 @@ Miscellaneous opcodes.
denoting nested loops, try statements, and such.
.. opcode:: POP_EXCEPT ()
Removes one block from the block stack. The popped block must be an exception
handler block, as implicitly created when entering an except handler.
In addition to popping extraneous values from the frame stack, the
last three popped values are used to restore the exception state.
.. opcode:: END_FINALLY ()
Terminates a :keyword:`finally` clause. The interpreter recalls whether the
@ -412,24 +420,22 @@ Miscellaneous opcodes.
.. opcode:: WITH_CLEANUP ()
Cleans up the stack when a :keyword:`with` statement block exits. On top of
the stack are 1--3 values indicating how/why the finally clause was entered:
Cleans up the stack when a :keyword:`with` statement block exits. TOS is
the context manager's :meth:`__exit__` bound method. Below TOS are 1--3
values indicating how/why the finally clause was entered:
* TOP = ``None``
* (TOP, SECOND) = (``WHY_{RETURN,CONTINUE}``), retval
* TOP = ``WHY_*``; no retval below it
* (TOP, SECOND, THIRD) = exc_info()
* SECOND = ``None``
* (SECOND, THIRD) = (``WHY_{RETURN,CONTINUE}``), retval
* SECOND = ``WHY_*``; no retval below it
* (SECOND, THIRD, FOURTH) = exc_info()
Under them is EXIT, the context manager's :meth:`__exit__` bound method.
In the last case, ``TOS(SECOND, THIRD, FOURTH)`` is called, otherwise
``TOS(None, None, None)``. In addition, TOS is removed from the stack.
In the last case, ``EXIT(TOP, SECOND, THIRD)`` is called, otherwise
``EXIT(None, None, None)``.
EXIT is removed from the stack, leaving the values above it in the same
order. In addition, if the stack represents an exception, *and* the function
call returns a 'true' value, this information is "zapped", to prevent
``END_FINALLY`` from re-raising the exception. (But non-local gotos should
still be resumed.)
If the stack represents an exception, *and* the function call returns
a 'true' value, this information is "zapped" and replaced with a single
``WHY_SILENCED`` to prevent ``END_FINALLY`` from re-raising the exception.
(But non-local gotos will still be resumed.)
.. XXX explain the WHY stuff!

11
Doc/library/inspect.rst
View File

@ -94,17 +94,6 @@ attributes:
| | f_code | code object being |
| | | executed in this frame |
+-----------+-----------------+---------------------------+
| | f_exc_traceback | traceback if raised in |
| | | this frame, or ``None`` |
+-----------+-----------------+---------------------------+
| | f_exc_type | exception type if raised |
| | | in this frame, or |
| | | ``None`` |
+-----------+-----------------+---------------------------+
| | f_exc_value | exception value if raised |
| | | in this frame, or |
| | | ``None`` |
+-----------+-----------------+---------------------------+
| | f_globals | global namespace seen by |
| | | this frame |
+-----------+-----------------+---------------------------+

4
Doc/library/sys.rst
View File

@ -136,8 +136,8 @@ always available.
frame is not handling an exception, the information is taken from the calling
stack frame, or its caller, and so on until a stack frame is found that is
handling an exception. Here, "handling an exception" is defined as "executing
or having executed an except clause." For any stack frame, only information
about the most recently handled exception is accessible.
an except clause." For any stack frame, only information about the exception
being currently handled is accessible.
.. index:: object: traceback

13
Doc/reference/datamodel.rst
View File

@ -875,19 +875,14 @@ Internal types
.. index::
single: f_trace (frame attribute)
single: f_exc_type (frame attribute)
single: f_exc_value (frame attribute)
single: f_exc_traceback (frame attribute)
single: f_lineno (frame attribute)
Special writable attributes: :attr:`f_trace`, if not ``None``, is a function
called at the start of each source code line (this is used by the debugger);
:attr:`f_exc_type`, :attr:`f_exc_value`, :attr:`f_exc_traceback` represent the
last exception raised in the parent frame provided another exception was ever
raised in the current frame (in all other cases they are None); :attr:`f_lineno`
is the current line number of the frame --- writing to this from within a trace
function jumps to the given line (only for the bottom-most frame). A debugger
can implement a Jump command (aka Set Next Statement) by writing to f_lineno.
:attr:`f_lineno` is the current line number of the frame --- writing to this
from within a trace function jumps to the given line (only for the bottom-most
frame). A debugger can implement a Jump command (aka Set Next Statement)
by writing to f_lineno.
Traceback objects
.. index::

14
Include/frameobject.h
View File

@ -27,13 +27,13 @@ typedef struct _frame {
PyObject **f_stacktop;
PyObject *f_trace; /* Trace function */
/* If an exception is raised in this frame, the next three are used to
* record the exception info (if any) originally in the thread state. See
* comments before set_exc_info() -- it's not obvious.
* Invariant: if _type is NULL, then so are _value and _traceback.
* Desired invariant: all three are NULL, or all three are non-NULL. That
* one isn't currently true, but "should be".
*/
/* In a generator, we need to be able to swap between the exception
state inside the generator and the exception state of the calling
frame (which shouldn't be impacted when the generator "yields"
from an except handler).
These three fields exist exactly for that, and are unused for
non-generator frames. See the SAVE_EXC_STATE and SWAP_EXC_STATE
macros in ceval.c for details of their use. */
PyObject *f_exc_type, *f_exc_value, *f_exc_traceback;
PyThreadState *f_tstate;

8
Include/opcode.h
View File

@ -70,6 +70,7 @@ extern "C" {
#define YIELD_VALUE 86
#define POP_BLOCK 87
#define END_FINALLY 88
#define POP_EXCEPT 89
#define HAVE_ARGUMENT 90 /* Opcodes from here have an argument: */
@ -133,6 +134,13 @@ extern "C" {
#define EXTENDED_ARG 143
/* EXCEPT_HANDLER is a special, implicit block type which is created when
entering an except handler. It is not an opcode but we define it here
as we want it to be available to both frameobject.c and ceval.c, while
remaining private.*/
#define EXCEPT_HANDLER 257
enum cmp_op {PyCmp_LT=Py_LT, PyCmp_LE=Py_LE, PyCmp_EQ=Py_EQ, PyCmp_NE=Py_NE, PyCmp_GT=Py_GT, PyCmp_GE=Py_GE,
PyCmp_IN, PyCmp_NOT_IN, PyCmp_IS, PyCmp_IS_NOT, PyCmp_EXC_MATCH, PyCmp_BAD};

7
Lib/doctest.py
View File

@ -1242,10 +1242,9 @@ class DocTestRunner:
# The example raised an exception: check if it was expected.
else:
exc_info = sys.exc_info()
exc_msg = traceback.format_exception_only(*exc_info[:2])[-1]
exc_msg = traceback.format_exception_only(*exception[:2])[-1]
if not quiet:
got += _exception_traceback(exc_info)
got += _exception_traceback(exception)
# If `example.exc_msg` is None, then we weren't expecting
# an exception.
@ -1275,7 +1274,7 @@ class DocTestRunner:
elif outcome is BOOM:
if not quiet:
self.report_unexpected_exception(out, test, example,
exc_info)
exception)
failures += 1
else:
assert False, ("unknown outcome", outcome)

3
Lib/inspect.py
View File

@ -197,9 +197,6 @@ def isframe(object):
f_back next outer frame object (this frame's caller)
f_builtins built-in namespace seen by this frame
f_code code object being executed in this frame
f_exc_traceback traceback if raised in this frame, or None
f_exc_type exception type if raised in this frame, or None
f_exc_value exception value if raised in this frame, or None
f_globals global namespace seen by this frame
f_lasti index of last attempted instruction in bytecode
f_lineno current line number in Python source code

1
Lib/opcode.py
View File

@ -105,6 +105,7 @@ def_op('MAKE_BYTES', 85)
def_op('YIELD_VALUE', 86)
def_op('POP_BLOCK', 87)
def_op('END_FINALLY', 88)
def_op('POP_EXCEPT', 89)
HAVE_ARGUMENT = 90 # Opcodes from here have an argument:

108
Lib/test/test_exceptions.py
View File

@ -427,6 +427,7 @@ class ExceptionTests(unittest.TestCase):
local_ref = obj
raise MyException(obj)
# Qualified "except" with "as"
obj = MyObj()
wr = weakref.ref(obj)
try:
@ -437,6 +438,113 @@ class ExceptionTests(unittest.TestCase):
obj = wr()
self.failUnless(obj is None, "%s" % obj)
# Qualified "except" without "as"
obj = MyObj()
wr = weakref.ref(obj)
try:
inner_raising_func()
except MyException:
pass
obj = None
obj = wr()
self.failUnless(obj is None, "%s" % obj)
# Bare "except"
obj = MyObj()
wr = weakref.ref(obj)
try:
inner_raising_func()
except:
pass
obj = None
obj = wr()
self.failUnless(obj is None, "%s" % obj)
# "except" with premature block leave
obj = MyObj()
wr = weakref.ref(obj)
for i in [0]:
try:
inner_raising_func()
except:
break
obj = None
obj = wr()
self.failUnless(obj is None, "%s" % obj)
# "except" block raising another exception
obj = MyObj()
wr = weakref.ref(obj)
try:
try:
inner_raising_func()
except:
raise KeyError
except KeyError:
obj = None
obj = wr()
self.failUnless(obj is None, "%s" % obj)
# Some complicated construct
obj = MyObj()
wr = weakref.ref(obj)
try:
inner_raising_func()
except MyException:
try:
try:
raise
finally:
raise
except MyException:
pass
obj = None
obj = wr()
self.failUnless(obj is None, "%s" % obj)
# Inside an exception-silencing "with" block
class Context:
def __enter__(self):
return self
def __exit__ (self, exc_type, exc_value, exc_tb):
return True
obj = MyObj()
wr = weakref.ref(obj)
with Context():
inner_raising_func()
obj = None
obj = wr()
self.failUnless(obj is None, "%s" % obj)
def test_generator_leaking(self):
# Test that generator exception state doesn't leak into the calling
# frame
def yield_raise():
try:
raise KeyError("caught")
except KeyError:
yield sys.exc_info()[0]
yield sys.exc_info()[0]
yield sys.exc_info()[0]
g = yield_raise()
self.assertEquals(next(g), KeyError)
self.assertEquals(sys.exc_info()[0], None)
self.assertEquals(next(g), KeyError)
self.assertEquals(sys.exc_info()[0], None)
self.assertEquals(next(g), None)
# Same test, but inside an exception handler
try:
raise TypeError("foo")
except TypeError:
g = yield_raise()
self.assertEquals(next(g), KeyError)
self.assertEquals(sys.exc_info()[0], TypeError)
self.assertEquals(next(g), KeyError)
self.assertEquals(sys.exc_info()[0], TypeError)
self.assertEquals(next(g), TypeError)
del g
self.assertEquals(sys.exc_info()[0], TypeError)
def test_main():
run_unittest(ExceptionTests)

73
Lib/test/test_raise.py
View File

@ -16,6 +16,13 @@ def get_tb():
return sys.exc_info()[2]
class Context:
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, exc_tb):
return True
class TestRaise(unittest.TestCase):
def test_invalid_reraise(self):
try:
@ -37,6 +44,71 @@ class TestRaise(unittest.TestCase):
else:
self.fail("No exception raised")
def test_except_reraise(self):
def reraise():
try:
raise TypeError("foo")
except:
try:
raise KeyError("caught")
except KeyError:
pass
raise
self.assertRaises(TypeError, reraise)
def test_finally_reraise(self):
def reraise():
try:
raise TypeError("foo")
except:
try:
raise KeyError("caught")
finally:
raise
self.assertRaises(KeyError, reraise)
def test_nested_reraise(self):
def nested_reraise():
raise
def reraise():
try:
raise TypeError("foo")
except:
nested_reraise()
self.assertRaises(TypeError, reraise)
def test_with_reraise1(self):
def reraise():
try:
raise TypeError("foo")
except:
with Context():
pass
raise
self.assertRaises(TypeError, reraise)
def test_with_reraise2(self):
def reraise():
try:
raise TypeError("foo")
except:
with Context():
raise KeyError("caught")
raise
self.assertRaises(TypeError, reraise)
def test_yield_reraise(self):
def reraise():
try:
raise TypeError("foo")
except:
yield 1
raise
g = reraise()
next(g)
self.assertRaises(TypeError, lambda: next(g))
self.assertRaises(StopIteration, lambda: next(g))
def test_erroneous_exception(self):
class MyException(Exception):
def __init__(self):
@ -158,6 +230,5 @@ class TestRemovedFunctionality(unittest.TestCase):
def test_main():
support.run_unittest(__name__)
if __name__ == "__main__":
unittest.main()

4
Misc/NEWS
View File

@ -49,6 +49,10 @@ Core and Builtins
Exception (KeyboardInterrupt, and SystemExit) propagate instead of
ignoring them.
- #3021 Exception reraising sematics have been significantly improved. However,
f_exc_type, f_exc_value, and f_exc_traceback cannot be accessed from Python
code anymore.
Extension Modules
-----------------

3
Misc/cheatsheet
View File

@ -1262,9 +1262,6 @@ Special informative state attributes for some types:
f_lineno (int, R/O): current line number
f_lasti (int, R/O): precise instruction (index into bytecode)
f_trace (function/None, R/W): debug hook called at start of each source line
f_exc_type (Type/None, R/W): Most recent exception type
f_exc_value (any, R/W): Most recent exception value
f_exc_traceback (traceback/None, R/W): Most recent exception traceback
Tracebacks:
tb_next (frame/None, R/O): next level in stack trace (toward the frame where
the exception occurred)

3
Objects/frameobject.c
View File

@ -20,9 +20,6 @@ static PyMemberDef frame_memberlist[] = {
{"f_builtins", T_OBJECT, OFF(f_builtins),READONLY},
{"f_globals", T_OBJECT, OFF(f_globals), READONLY},
{"f_lasti", T_INT, OFF(f_lasti), READONLY},
{"f_exc_type", T_OBJECT, OFF(f_exc_type)},
{"f_exc_value", T_OBJECT, OFF(f_exc_value)},
{"f_exc_traceback", T_OBJECT, OFF(f_exc_traceback)},
{NULL} /* Sentinel */
};

369
Python/ceval.c
View File

@ -116,8 +116,6 @@ static int maybe_call_line_trace(Py_tracefunc, PyObject *,
static PyObject * cmp_outcome(int, PyObject *, PyObject *);
static PyObject * import_from(PyObject *, PyObject *);
static int import_all_from(PyObject *, PyObject *);
static void set_exc_info(PyThreadState *, PyObject *, PyObject *, PyObject *);
static void reset_exc_info(PyThreadState *);
static void format_exc_check_arg(PyObject *, const char *, PyObject *);
static PyObject * unicode_concatenate(PyObject *, PyObject *,
PyFrameObject *, unsigned char *);
@ -483,7 +481,8 @@ enum why_code {
WHY_RETURN = 0x0008, /* 'return' statement */
WHY_BREAK = 0x0010, /* 'break' statement */
WHY_CONTINUE = 0x0020, /* 'continue' statement */
WHY_YIELD = 0x0040 /* 'yield' operator */
WHY_YIELD = 0x0040, /* 'yield' operator */
WHY_SILENCED = 0x0080 /* Exception silenced by 'with' */
};
static enum why_code do_raise(PyObject *, PyObject *);
@ -692,6 +691,53 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
GETLOCAL(i) = value; \
Py_XDECREF(tmp); } while (0)
#define UNWIND_BLOCK(b) \
while (STACK_LEVEL() > (b)->b_level) { \
PyObject *v = POP(); \
Py_XDECREF(v); \
}
#define UNWIND_EXCEPT_HANDLER(b) \
assert(STACK_LEVEL() >= (b)->b_level + 3); \
while (STACK_LEVEL() > (b)->b_level + 3) { \
PyObject *v = POP(); \
Py_XDECREF(v); \
} \
Py_XDECREF(tstate->exc_type); \
tstate->exc_type = POP(); \
Py_XDECREF(tstate->exc_value); \
tstate->exc_value = POP(); \
Py_XDECREF(tstate->exc_traceback); \
tstate->exc_traceback = POP();
#define SAVE_EXC_STATE() \
{ \
Py_XINCREF(tstate->exc_type); \
Py_XINCREF(tstate->exc_value); \
Py_XINCREF(tstate->exc_traceback); \
Py_XDECREF(f->f_exc_type); \
Py_XDECREF(f->f_exc_value); \
Py_XDECREF(f->f_exc_traceback); \
f->f_exc_type = tstate->exc_type; \
f->f_exc_value = tstate->exc_value; \
f->f_exc_traceback = tstate->exc_traceback; \
}
#define SWAP_EXC_STATE() \
{ \
PyObject *tmp; \
tmp = tstate->exc_type; \
tstate->exc_type = f->f_exc_type; \
f->f_exc_type = tmp; \
tmp = tstate->exc_value; \
tstate->exc_value = f->f_exc_value; \
f->f_exc_value = tmp; \
tmp = tstate->exc_traceback; \
tstate->exc_traceback = f->f_exc_traceback; \
f->f_exc_traceback = tmp; \
}
/* Start of code */
if (f == NULL)
@ -765,6 +811,18 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
assert(stack_pointer != NULL);
f->f_stacktop = NULL; /* remains NULL unless yield suspends frame */
if (f->f_code->co_flags & CO_GENERATOR) {
if (f->f_exc_type != NULL && f->f_exc_type != Py_None) {
/* We were in an except handler when we left,
restore the exception state which was put aside
(see YIELD_VALUE). */
SWAP_EXC_STATE();
}
else {
SAVE_EXC_STATE();
}
}
#ifdef LLTRACE
lltrace = PyDict_GetItemString(f->f_globals, "__lltrace__") != NULL;
#endif
@ -1443,15 +1501,29 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
retval = POP();
f->f_stacktop = stack_pointer;
why = WHY_YIELD;
/* Put aside the current exception state and restore
that of the calling frame. This only serves when
"yield" is used inside an except handler. */
SWAP_EXC_STATE();
goto fast_yield;
case POP_EXCEPT:
{
PyTryBlock *b = PyFrame_BlockPop(f);
if (b->b_type != EXCEPT_HANDLER) {
PyErr_SetString(PyExc_SystemError,
"popped block is not an except handler");
why = WHY_EXCEPTION;
break;
}
UNWIND_EXCEPT_HANDLER(b);
}
continue;
case POP_BLOCK:
{
PyTryBlock *b = PyFrame_BlockPop(f);
while (STACK_LEVEL() > b->b_level) {
v = POP();
Py_DECREF(v);
}
UNWIND_BLOCK(b);
}
continue;
@ -1464,6 +1536,22 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
if (why == WHY_RETURN ||
why == WHY_CONTINUE)
retval = POP();
if (why == WHY_SILENCED) {
/* An exception was silenced by 'with', we must
manually unwind the EXCEPT_HANDLER block which was
created when the exception was caught, otherwise
the stack will be in an inconsistent state. */
PyTryBlock *b = PyFrame_BlockPop(f);
if (b->b_type != EXCEPT_HANDLER) {
PyErr_SetString(PyExc_SystemError,
"popped block is not an except handler");
why = WHY_EXCEPTION;
}
else {
UNWIND_EXCEPT_HANDLER(b);
why = WHY_NOT;
}
}
}
else if (PyExceptionClass_Check(v)) {
w = POP();
@ -1477,19 +1565,6 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
"'finally' pops bad exception");
why = WHY_EXCEPTION;
}
/*
Make sure the exception state is cleaned up before
the end of an except block. This ensures objects
referenced by the exception state are not kept
alive too long.
See #2507.
*/
if (tstate->frame->f_exc_type != NULL)
reset_exc_info(tstate);
else {
assert(tstate->frame->f_exc_value == NULL);
assert(tstate->frame->f_exc_traceback == NULL);
}
Py_DECREF(v);
break;
@ -2056,59 +2131,33 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
should still be resumed.)
*/
PyObject *exit_func;
u = POP();
PyObject *exit_func = POP();
u = TOP();
if (u == Py_None) {
exit_func = TOP();
SET_TOP(u);
v = w = Py_None;
}
else if (PyLong_Check(u)) {
switch(PyLong_AS_LONG(u)) {
case WHY_RETURN:
case WHY_CONTINUE:
/* Retval in TOP. */
exit_func = SECOND();
SET_SECOND(TOP());
SET_TOP(u);
break;
default:
exit_func = TOP();
SET_TOP(u);
break;
}
u = v = w = Py_None;
}
else {
v = TOP();
w = SECOND();
exit_func = THIRD();
SET_TOP(u);
SET_SECOND(v);
SET_THIRD(w);
v = SECOND();
w = THIRD();
}
/* XXX Not the fastest way to call it... */
x = PyObject_CallFunctionObjArgs(exit_func, u, v, w,
NULL);
if (x == NULL) {
Py_DECREF(exit_func);
if (x == NULL)
break; /* Go to error exit */
}
if (u != Py_None && PyObject_IsTrue(x)) {
/* There was an exception and a true return */
/* There was an exception and a True return */
STACKADJ(-2);
Py_INCREF(Py_None);
SET_TOP(Py_None);
SET_TOP(PyLong_FromLong((long) WHY_SILENCED));
Py_DECREF(u);
Py_DECREF(v);
Py_DECREF(w);
} else {
/* The stack was rearranged to remove EXIT
above. Let END_FINALLY do its thing */
}
Py_DECREF(x);
Py_DECREF(exit_func);
PREDICT(END_FINALLY);
break;
}
@ -2370,50 +2419,63 @@ fast_block_end:
break;
}
while (STACK_LEVEL() > b->b_level) {
v = POP();
Py_XDECREF(v);
if (b->b_type == EXCEPT_HANDLER) {
UNWIND_EXCEPT_HANDLER(b);
if (why == WHY_EXCEPTION) {
Py_CLEAR(tstate->exc_type);
Py_CLEAR(tstate->exc_value);
Py_CLEAR(tstate->exc_traceback);
}
continue;
}
UNWIND_BLOCK(b);
if (b->b_type == SETUP_LOOP && why == WHY_BREAK) {
why = WHY_NOT;
JUMPTO(b->b_handler);
break;
}
if (b->b_type == SETUP_FINALLY ||
(b->b_type == SETUP_EXCEPT &&
why == WHY_EXCEPTION)) {
if (why == WHY_EXCEPTION) {
if (why == WHY_EXCEPTION && (b->b_type == SETUP_EXCEPT
|| b->b_type == SETUP_FINALLY)) {
PyObject *exc, *val, *tb;
PyErr_Fetch(&exc, &val, &tb);
if (val == NULL) {
val = Py_None;
Py_INCREF(val);
int handler = b->b_handler;
/* Beware, this invalidates all b->b_* fields */
PyFrame_BlockSetup(f, EXCEPT_HANDLER, -1, STACK_LEVEL());
PUSH(tstate->exc_traceback);
PUSH(tstate->exc_value);
if (tstate->exc_type != NULL) {
PUSH(tstate->exc_type);
}
else {
Py_INCREF(Py_None);
PUSH(Py_None);
}
PyErr_Fetch(&exc, &val, &tb);
/* Make the raw exception data
available to the handler,
so a program can emulate the
Python main loop. Don't do
this for 'finally'. */
if (b->b_type == SETUP_EXCEPT) {
Python main loop. */
PyErr_NormalizeException(
&exc, &val, &tb);
set_exc_info(tstate,
exc, val, tb);
}
if (tb == NULL) {
Py_INCREF(Py_None);
PUSH(Py_None);
} else
PyException_SetTraceback(val, tb);
Py_INCREF(exc);
tstate->exc_type = exc;
Py_INCREF(val);
tstate->exc_value = val;
tstate->exc_traceback = tb;
if (tb == NULL)
tb = Py_None;
Py_INCREF(tb);
PUSH(tb);
PUSH(val);
PUSH(exc);
why = WHY_NOT;
JUMPTO(handler);
break;
}
else {
if (b->b_type == SETUP_FINALLY) {
if (why & (WHY_RETURN | WHY_CONTINUE))
PUSH(retval);
v = PyLong_FromLong((long)why);
PUSH(v);
}
PUSH(PyLong_FromLong((long)why));
why = WHY_NOT;
JUMPTO(b->b_handler);
break;
@ -2471,13 +2533,6 @@ fast_yield:
}
}
if (tstate->frame->f_exc_type != NULL)
reset_exc_info(tstate);
else {
assert(tstate->frame->f_exc_value == NULL);
assert(tstate->frame->f_exc_traceback == NULL);
}
/* pop frame */
exit_eval_frame:
Py_LeaveRecursiveCall();
@ -2757,150 +2812,6 @@ fail: /* Jump here from prelude on failure */
}
/* Implementation notes for set_exc_info() and reset_exc_info():
- Below, 'exc_ZZZ' stands for 'exc_type', 'exc_value' and
'exc_traceback'. These always travel together.
- tstate->curexc_ZZZ is the "hot" exception that is set by
PyErr_SetString(), cleared by PyErr_Clear(), and so on.
- Once an exception is caught by an except clause, it is transferred
from tstate->curexc_ZZZ to tstate->exc_ZZZ, from which sys.exc_info()
can pick it up. This is the primary task of set_exc_info().
XXX That can't be right: set_exc_info() doesn't look at tstate->curexc_ZZZ.
- Now let me explain the complicated dance with frame->f_exc_ZZZ.
Long ago, when none of this existed, there were just a few globals:
one set corresponding to the "hot" exception, and one set
corresponding to sys.exc_ZZZ. (Actually, the latter weren't C
globals; they were simply stored as sys.exc_ZZZ. For backwards
compatibility, they still are!) The problem was that in code like
this:
try:
"something that may fail"
except "some exception":
"do something else first"
"print the exception from sys.exc_ZZZ."
if "do something else first" invoked something that raised and caught
an exception, sys.exc_ZZZ were overwritten. That was a frequent
cause of subtle bugs. I fixed this by changing the semantics as
follows:
- Within one frame, sys.exc_ZZZ will hold the last exception caught
*in that frame*.
- But initially, and as long as no exception is caught in a given
frame, sys.exc_ZZZ will hold the last exception caught in the
previous frame (or the frame before that, etc.).
The first bullet fixed the bug in the above example. The second
bullet was for backwards compatibility: it was (and is) common to
have a function that is called when an exception is caught, and to
have that function access the caught exception via sys.exc_ZZZ.
(Example: traceback.print_exc()).
At the same time I fixed the problem that sys.exc_ZZZ weren't
thread-safe, by introducing sys.exc_info() which gets it from tstate;
but that's really a separate improvement.
The reset_exc_info() function in ceval.c restores the tstate->exc_ZZZ
variables to what they were before the current frame was called. The
set_exc_info() function saves them on the frame so that
reset_exc_info() can restore them. The invariant is that
frame->f_exc_ZZZ is NULL iff the current frame never caught an
exception (where "catching" an exception applies only to successful
except clauses); and if the current frame ever caught an exception,
frame->f_exc_ZZZ is the exception that was stored in tstate->exc_ZZZ
at the start of the current frame.
*/
static void
set_exc_info(PyThreadState *tstate,
PyObject *type, PyObject *value, PyObject *tb)
{
PyFrameObject *frame = tstate->frame;
PyObject *tmp_type, *tmp_value, *tmp_tb;
assert(type != NULL);
assert(frame != NULL);
if (frame->f_exc_type == NULL) {
assert(frame->f_exc_value == NULL);
assert(frame->f_exc_traceback == NULL);
/* This frame didn't catch an exception before. */
/* Save previous exception of this thread in this frame. */
if (tstate->exc_type == NULL) {
/* XXX Why is this set to Py_None? */
Py_INCREF(Py_None);
tstate->exc_type = Py_None;
}
Py_INCREF(tstate->exc_type);
Py_XINCREF(tstate->exc_value);
Py_XINCREF(tstate->exc_traceback);
frame->f_exc_type = tstate->exc_type;
frame->f_exc_value = tstate->exc_value;
frame->f_exc_traceback = tstate->exc_traceback;
}
/* Set new exception for this thread. */
tmp_type = tstate->exc_type;
tmp_value = tstate->exc_value;
tmp_tb = tstate->exc_traceback;
Py_INCREF(type);
Py_XINCREF(value);
Py_XINCREF(tb);
tstate->exc_type = type;
tstate->exc_value = value;
tstate->exc_traceback = tb;
PyException_SetTraceback(value, tb);
Py_XDECREF(tmp_type);
Py_XDECREF(tmp_value);
Py_XDECREF(tmp_tb);
}
static void
reset_exc_info(PyThreadState *tstate)
{
PyFrameObject *frame;
PyObject *tmp_type, *tmp_value, *tmp_tb;
/* It's a precondition that the thread state's frame caught an
* exception -- verify in a debug build.
*/
assert(tstate != NULL);
frame = tstate->frame;
assert(frame != NULL);
assert(frame->f_exc_type != NULL);
/* Copy the frame's exception info back to the thread state. */
tmp_type = tstate->exc_type;
tmp_value = tstate->exc_value;
tmp_tb = tstate->exc_traceback;
Py_INCREF(frame->f_exc_type);
Py_XINCREF(frame->f_exc_value);
Py_XINCREF(frame->f_exc_traceback);
tstate->exc_type = frame->f_exc_type;
tstate->exc_value = frame->f_exc_value;
tstate->exc_traceback = frame->f_exc_traceback;
Py_XDECREF(tmp_type);
Py_XDECREF(tmp_value);
Py_XDECREF(tmp_tb);
/* Clear the frame's exception info. */
tmp_type = frame->f_exc_type;
tmp_value = frame->f_exc_value;
tmp_tb = frame->f_exc_traceback;
frame->f_exc_type = NULL;
frame->f_exc_value = NULL;
frame->f_exc_traceback = NULL;
Py_DECREF(tmp_type);
Py_XDECREF(tmp_value);
Py_XDECREF(tmp_tb);
}
/* Logic for the raise statement (too complicated for inlining).
This *consumes* a reference count to each of its arguments. */
static enum why_code

29
Python/compile.c
View File

@ -760,6 +760,8 @@ opcode_stack_effect(int opcode, int oparg)
case POP_BLOCK:
return 0;
case POP_EXCEPT:
return 0; /* -3 except if bad bytecode */
case END_FINALLY:
return -1; /* or -2 or -3 if exception occurred */
@ -818,7 +820,8 @@ opcode_stack_effect(int opcode, int oparg)
return 0;
case SETUP_EXCEPT:
case SETUP_FINALLY:
return 3; /* actually pushed by an exception */
return 6; /* can push 3 values for the new exception
+ 3 others for the previous exception state */
case LOAD_FAST:
return 1;
@ -2031,6 +2034,7 @@ compiler_try_except(struct compiler *c, stmt_ty s)
/* second # body */
VISIT_SEQ(c, stmt, handler->v.ExceptHandler.body);
ADDOP(c, POP_BLOCK);
ADDOP(c, POP_EXCEPT);
compiler_pop_fblock(c, FINALLY_TRY, cleanup_body);
/* finally: */
@ -2050,9 +2054,20 @@ compiler_try_except(struct compiler *c, stmt_ty s)
compiler_pop_fblock(c, FINALLY_END, cleanup_end);
}
else {
basicblock *cleanup_body;
cleanup_body = compiler_new_block(c);
if(!cleanup_body)
return 0;
ADDOP(c, POP_TOP);
ADDOP(c, POP_TOP);
compiler_use_next_block(c, cleanup_body);
if (!compiler_push_fblock(c, FINALLY_TRY, cleanup_body))
return 0;
VISIT_SEQ(c, stmt, handler->v.ExceptHandler.body);
ADDOP(c, POP_EXCEPT);
compiler_pop_fblock(c, FINALLY_TRY, cleanup_body);
}
ADDOP_JREL(c, JUMP_FORWARD, end);
compiler_use_next_block(c, except);
@ -3109,7 +3124,7 @@ compiler_with(struct compiler *c, stmt_ty s)
{
static identifier enter_attr, exit_attr;
basicblock *block, *finally;
identifier tmpvalue = NULL;
identifier tmpvalue = NULL, tmpexit = NULL;
assert(s->kind == With_kind);
@ -3144,6 +3159,10 @@ compiler_with(struct compiler *c, stmt_ty s)
return 0;
PyArena_AddPyObject(c->c_arena, tmpvalue);
}
tmpexit = compiler_new_tmpname(c);
if (tmpexit == NULL)
return 0;
PyArena_AddPyObject(c->c_arena, tmpexit);
/* Evaluate EXPR */
VISIT(c, expr, s->v.With.context_expr);
@ -3151,7 +3170,8 @@ compiler_with(struct compiler *c, stmt_ty s)
/* Squirrel away context.__exit__ by stuffing it under context */
ADDOP(c, DUP_TOP);
ADDOP_O(c, LOAD_ATTR, exit_attr, names);
ADDOP(c, ROT_TWO);
if (!compiler_nameop(c, tmpexit, Store))
return 0;
/* Call context.__enter__() */
ADDOP_O(c, LOAD_ATTR, enter_attr, names);
@ -3198,6 +3218,9 @@ compiler_with(struct compiler *c, stmt_ty s)
/* Finally block starts; context.__exit__ is on the stack under
the exception or return information. Just issue our magic
opcode. */
if (!compiler_nameop(c, tmpexit, Load) ||
!compiler_nameop(c, tmpexit, Del))
return 0;
ADDOP(c, WITH_CLEANUP);
/* Finally block ends. */

3
Python/import.c
View File

@ -86,8 +86,9 @@ extern time_t PyOS_GetLastModificationTime(char *, FILE *);
3100 (merge from 2.6a0, see 62151)
3102 (__file__ points to source file)
Python 3.0a4: 3110 (WITH_CLEANUP optimization).
Python 3.0a5: 3130 (lexical exception stacking, including POP_EXCEPT)
*/
#define MAGIC (3110 | ((long)'\r'<<16) | ((long)'\n'<<24))
#define MAGIC (3130 | ((long)'\r'<<16) | ((long)'\n'<<24))
/* Magic word as global; note that _PyImport_Init() can change the
value of this global to accommodate for alterations of how the