How to extract a string from a Python 3 exception via the C API

Question

I have some C++ code that runs Python 3 code using Boost.Python. If any exception in Python occurs, it is caught and a C++ exception thrown. I want to pass some minimal error information to the C++ exception.

What I currently have is this:

try {
    // execute python code via Boost.Python
} catch(boost::python::error_already_set&) {
    PyObject *ptype, *pvalue, *ptraceback;
    PyErr_Fetch(&ptype, &pvalue, &ptraceback);
    if(pvalue) {
        // ???
    }
}

There are many helpful answers here at SO, but they all seem to apply to Python 2, and their solutions do not work anymore. I have tried a few things like PyBytes_AsString, PyUnicode_AsUTF8, but all I get back are null pointers.

How do I go about extracting something meaningful from pvalue? For starters, the type name of the exception raised would already be quite helpful. If there was a string passed to the exception, getting that would be most helpful.

sbi · Accepted Answer · 2018-03-26 11:04:49Z

4

Of course, I found a solution myself immediately after I had formulated and posted this question.

This code finally does the trick and provides nice messages:

try {
    // execute python code via Boost.Python
} catch(boost::python::error_already_set&) {
    PyObject *ptype, *pvalue, *ptraceback;
    PyErr_Fetch(&ptype, &pvalue, &ptraceback);
    if(pvalue) {
        PyObject *pstr = PyObject_Str(pvalue);
        if(pstr) {
            const char* err_msg = PyUnicode_AsUTF8(pstr);
            if(pstr)
                // use err_msg
        }
        PyErr_Restore(ptype, pvalue, ptraceback);
    }
}

I'd be glad for any feedback, though. I know little of Python and less of its C API.

edited Mar 26, 2018 at 11:04

answered Mar 23, 2018 at 14:29

sbi

225k46 gold badges267 silver badges447 bronze badges

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

1 Comment

Jiminion Over a year ago

PyObject_Str() creates a new reference. I am trying to do the same thing, but using PyBytes_AsString()

Collectives™ on Stack Overflow

How to extract a string from a Python 3 exception via the C API

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related