getting a error message with Python/C API

Question

I was looking for a way to get error message from executing python code in C++. I tried some answers from How to get Python exception text, but any of them worked for me. Can someone explain me what I'm doing wrong?

#include <iostream>
#include <Python.h>

int main() {
    Py_Initialize();
    if (PyRun_SimpleString("something stupid")) {
        PyObject *ptype, *pvalue, *ptraceback;
        PyErr_Fetch(&ptype, &pvalue, &ptraceback);
        const char *errMsg = PyUnicode_AsUTF8(PyObject_Str(ptraceback));
        std::cout << errMsg;
    }
    Py_Finalize();
}

I expect to print something like that:

  File "<string>", line 1
something stupid
          ^
SyntaxError: invalid syntax

But when I run code, cout prints:

<NULL>

There's a lot of error checking that you're missing tht you might help. Check if ptraceback is NULL. Check if the result of PyObject_Str(ptraceback) is NULL. — DavidW
– DavidW, Commented Jul 23, 2021 at 7:42

IzZy · Accepted Answer · 2021-07-23 09:21:29Z

0

According to documentation (https://docs.python.org/3/c-api/veryhigh.html#c.PyRun_SimpleStringFlags), when using PyRun_SimpleStringFlags() (or just PyRun_SimpleString()):

If there was an error, there is no way to get the exception information.

So code must be runned the other way. Eventually, you can run in interpreter:

PyRun_SimpleString("import traceback, sys");
PyRun_SimpleString("trace = ''.join(traceback.format_exception(sys.last_type, sys.last_value, sys.last_traceback))");

Then read trace from interpreter, similar like in this answer https://stackoverflow.com/a/63320285/13966135 .

answered Jul 23, 2021 at 9:21

IzZy

3944 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

getting a error message with Python/C API

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related