Adding extra frames to traceback in C module

[Roger Binns]

One thing I would like to do in my extension module is
add extra frames to the traceback when an extension
occurs. At the moment C code is invisible to tracebacks.
This is relevant when the C code makes a Python callback.
For example if the following code sequence happens
(time going down)

Python C

A
B
C
D
E
F
G
H

If there is an exception in H then the traceback seen
from A will be "B C G H". I want to get D, E and F
into there as well. This is because "G H" could be
called for several different reasons in the C code
and adding the extra information will establish why.

I couldn't find anything on the web or in the documentation
to explain how to do it. I did find snippets of code
doing things like PyTraceback_Her e but they use a real
Python frame which I don't have and don't know how to
synthesize.

Roger

[John Machin]

Re: Adding extra frames to traceback in C module

On 10/06/2006 1:24 PM, Roger Binns wrote:[color=blue]
> One thing I would like to do in my extension module is
> add extra frames to the traceback when an extension
> occurs. At the moment C code is invisible to tracebacks.
> This is relevant when the C code makes a Python callback.[/color]

[snip]
[color=blue]
> I couldn't find anything on the web or in the documentation
> to explain how to do it. I did find snippets of code
> doing things like PyTraceback_Her e but they use a real
> Python frame which I don't have and don't know how to
> synthesize.[/color]

In the C code generated by Pyrex, the frame is faked up on the fly if an
error occurs:

C:\junk>demotrb ackmain.py
Traceback (most recent call last):
File "C:\junk\demotr backmain.py", line 12, in ?
funcb()
File "C:\junk\demotr backmain.py", line 3, in funcb
demotrback.func c(funce)
File "demotrback.pyx ", line 2, in demotrback.func c
funcd1(cbfunc)
File "demotrback.pyx ", line 5, in demotrback.func d1
funcd2(callb)
File "demotrback.pyx ", line 8, in demotrback.func d2
callb()
File "C:\junk\demotr backmain.py", line 6, in funce
funcf()
File "C:\junk\demotr backmain.py", line 9, in funcf
x = 1 / 0
ZeroDivisionErr or: integer division or modulo by zero

Check out

http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/version/Doc/overview.html#ExceptionValues

then whip up some quick examples and look at the generated code.

HTH,
John

[greg]

Re: Adding extra frames to traceback in C module

Roger Binns wrote:[color=blue]
> One thing I would like to do in my extension module is
> add extra frames to the traceback when an extension
> occurs.
>
> I did find snippets of code
> doing things like PyTraceback_Her e but they use a real
> Python frame which I don't have and don't know how to
> synthesize.[/color]

This is the code Pyrex uses to add frames to the traceback.
It creates a fake frame object and fills in just enough
of it to keep the traceback printing code happy.

Or you could just use Pyrex for your extension module
in the first place, and get it done for you automatically.

-----------------------------------------------------------
#include "compile.h"
#include "frameobjec t.h"
#include "traceback. h"

static void __Pyx_AddTraceb ack(char *funcname) {
PyObject *py_srcfile = 0;
PyObject *py_funcname = 0;
PyObject *py_globals = 0;
PyObject *empty_tuple = 0;
PyObject *empty_string = 0;
PyCodeObject *py_code = 0;
PyFrameObject *py_frame = 0;

py_srcfile = PyString_FromSt ring(%(FILENAME )s);
if (!py_srcfile) goto bad;
py_funcname = PyString_FromSt ring(funcname);
if (!py_funcname) goto bad;
py_globals = PyModule_GetDic t(%(GLOBALS)s);
if (!py_globals) goto bad;
empty_tuple = PyTuple_New(0);
if (!empty_tuple) goto bad;
empty_string = PyString_FromSt ring("");
if (!empty_string) goto bad;
py_code = PyCode_New(
0, /*int argcount,*/
0, /*int nlocals,*/
0, /*int stacksize,*/
0, /*int flags,*/
empty_string, /*PyObject *code,*/
empty_tuple, /*PyObject *consts,*/
empty_tuple, /*PyObject *names,*/
empty_tuple, /*PyObject *varnames,*/
empty_tuple, /*PyObject *freevars,*/
empty_tuple, /*PyObject *cellvars,*/
py_srcfile, /*PyObject *filename,*/
py_funcname, /*PyObject *name,*/
%(LINENO)s, /*int firstlineno,*/
empty_string /*PyObject *lnotab*/
);
if (!py_code) goto bad;
py_frame = PyFrame_New(
PyThreadState_G et(), /*PyThreadState *tstate,*/
py_code, /*PyCodeObject *code,*/
py_globals, /*PyObject *globals,*/
0 /*PyObject *locals*/
);
if (!py_frame) goto bad;
py_frame->f_lineno = %(LINENO)s;
PyTraceBack_Her e(py_frame);
bad:
Py_XDECREF(py_s rcfile);
Py_XDECREF(py_f uncname);
Py_XDECREF(empt y_tuple);
Py_XDECREF(empt y_string);
Py_XDECREF(py_c ode);
Py_XDECREF(py_f rame);
}

--
Greg