finally:
del frame
+ If you want to keep the frame around (for example to print a traceback
+ later), you can also break reference cycles by using the
+ :meth:`frame.clear` method.
+
The optional *context* argument supported by most of these functions specifies
the number of lines of context to return, which are centered around the current
line.
frame). A debugger can implement a Jump command (aka Set Next Statement)
by writing to f_lineno.
+ Frame objects support one method:
+
+ .. method:: frame.clear()
+
+ This method clears all references to local variables held by the
+ frame. Also, if the frame belonged to a generator, the generator
+ is finalized. This helps break reference cycles involving frame
+ objects (for example when catching an exception and storing its
+ traceback for later use).
+
+ :exc:`RuntimeError` is raised if the frame is currently executing.
+
+ .. versionadded:: 3.4
+
Traceback objects
.. index::
object: traceback
non-generator frames. See the save_exc_state and swap_exc_state
functions in ceval.c for details of their use. */
PyObject *f_exc_type, *f_exc_value, *f_exc_traceback;
+ /* Borrowed referenced to a generator, or NULL */
+ PyObject *f_gen;
PyThreadState *f_tstate;
int f_lasti; /* Last instruction if called */
bytecode index. */
int f_lineno; /* Current line number */
int f_iblock; /* index in f_blockstack */
+ char f_executing; /* whether the frame is still executing */
PyTryBlock f_blockstack[CO_MAXBLOCKS]; /* for try and loop blocks */
PyObject *f_localsplus[1]; /* locals+stack, dynamically sized */
} PyFrameObject;
PyAPI_FUNC(int) PyGen_NeedsFinalizing(PyGenObject *);
PyAPI_FUNC(int) _PyGen_FetchStopIterationValue(PyObject **);
PyObject *_PyGen_Send(PyGenObject *, PyObject *);
+PyAPI_FUNC(void) _PyGen_Finalize(PyObject *self);
+
#ifdef __cplusplus
}
nfrees = len(x.f_code.co_freevars)
extras = x.f_code.co_stacksize + x.f_code.co_nlocals +\
ncells + nfrees - 1
- check(x, vsize('12P3i' + CO_MAXBLOCKS*'3i' + 'P' + extras*'P'))
+ check(x, vsize('13P3ic' + CO_MAXBLOCKS*'3i' + 'P' + extras*'P'))
# function
def func(): pass
check(func, size('12P'))
class TracebackFormatTests(unittest.TestCase):
- def test_traceback_format(self):
+ def some_exception(self):
+ raise KeyError('blah')
+
+ def check_traceback_format(self, cleanup_func=None):
try:
- raise KeyError('blah')
+ self.some_exception()
except KeyError:
type_, value, tb = sys.exc_info()
+ if cleanup_func is not None:
+ # Clear the inner frames, not this one
+ cleanup_func(tb.tb_next)
traceback_fmt = 'Traceback (most recent call last):\n' + \
''.join(traceback.format_tb(tb))
file_ = StringIO()
# Make sure that the traceback is properly indented.
tb_lines = python_fmt.splitlines()
- self.assertEqual(len(tb_lines), 3)
- banner, location, source_line = tb_lines
+ self.assertEqual(len(tb_lines), 5)
+ banner = tb_lines[0]
+ location, source_line = tb_lines[-2:]
self.assertTrue(banner.startswith('Traceback'))
self.assertTrue(location.startswith(' File'))
self.assertTrue(source_line.startswith(' raise'))
+ def test_traceback_format(self):
+ self.check_traceback_format()
+
+ def test_traceback_format_with_cleared_frames(self):
+ # Check that traceback formatting also works with a clear()ed frame
+ def cleanup_tb(tb):
+ tb.tb_frame.clear()
+ self.check_traceback_format(cleanup_tb)
+
def test_stack_format(self):
# Verify _stack functions. Note we have to use _getframe(1) to
# compare them without this frame appearing in the output
Core and Builtins
-----------------
+- Issue #17934: Add a clear() method to frame objects, to help clean up
+ expensive details (local variables) and break reference cycles.
+
Library
-------
}
static void
-frame_clear(PyFrameObject *f)
+frame_tp_clear(PyFrameObject *f)
{
PyObject **fastlocals, **p, **oldtop;
Py_ssize_t i, slots;
*/
oldtop = f->f_stacktop;
f->f_stacktop = NULL;
+ f->f_executing = 0;
Py_CLEAR(f->f_exc_type);
Py_CLEAR(f->f_exc_value);
}
}
+static PyObject *
+frame_clear(PyFrameObject *f)
+{
+ if (f->f_executing) {
+ PyErr_SetString(PyExc_RuntimeError,
+ "cannot clear an executing frame");
+ return NULL;
+ }
+ if (f->f_gen) {
+ _PyGen_Finalize(f->f_gen);
+ assert(f->f_gen == NULL);
+ }
+ frame_tp_clear(f);
+ Py_RETURN_NONE;
+}
+
+PyDoc_STRVAR(clear__doc__,
+"F.clear(): clear most references held by the frame");
+
static PyObject *
frame_sizeof(PyFrameObject *f)
{
"F.__sizeof__() -> size of F in memory, in bytes");
static PyMethodDef frame_methods[] = {
+ {"clear", (PyCFunction)frame_clear, METH_NOARGS,
+ clear__doc__},
{"__sizeof__", (PyCFunction)frame_sizeof, METH_NOARGS,
sizeof__doc__},
{NULL, NULL} /* sentinel */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,/* tp_flags */
0, /* tp_doc */
(traverseproc)frame_traverse, /* tp_traverse */
- (inquiry)frame_clear, /* tp_clear */
+ (inquiry)frame_tp_clear, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
f->f_lasti = -1;
f->f_lineno = code->co_firstlineno;
f->f_iblock = 0;
+ f->f_executing = 0;
+ f->f_gen = NULL;
_PyObject_GC_TRACK(f);
return f;
return 0;
}
-static void
-gen_finalize(PyObject *self)
+void
+_PyGen_Finalize(PyObject *self)
{
PyGenObject *gen = (PyGenObject *)self;
PyObject *res;
Py_XDECREF(t);
Py_XDECREF(v);
Py_XDECREF(tb);
+ gen->gi_frame->f_gen = NULL;
gen->gi_frame = NULL;
Py_DECREF(f);
}
0, /* tp_weaklist */
0, /* tp_del */
0, /* tp_version_tag */
- gen_finalize, /* tp_finalize */
+ _PyGen_Finalize, /* tp_finalize */
};
PyObject *
return NULL;
}
gen->gi_frame = f;
+ f->f_gen = (PyObject *) gen;
Py_INCREF(f->f_code);
gen->gi_code = (PyObject *)(f->f_code);
gen->gi_running = 0;
stack_pointer = f->f_stacktop;
assert(stack_pointer != NULL);
f->f_stacktop = NULL; /* remains NULL unless yield suspends frame */
+ f->f_executing = 1;
if (co->co_flags & CO_GENERATOR && !throwflag) {
if (f->f_exc_type != NULL && f->f_exc_type != Py_None) {
/* pop frame */
exit_eval_frame:
Py_LeaveRecursiveCall();
+ f->f_executing = 0;
tstate->frame = f->f_back;
return retval;
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