问题
I want to embed python in my C++ application. I'm using Boost library - great tool. But i have one problem.
If python function throws an exception, i want to catch it and print error in my application or get some detailed information like line number in python script that caused error.
How can i do it? I can't find any functions to get detailed exception information in Python API or Boost.
try {
module=import("MyModule"); //this line will throw excetion if MyModule contains an error
} catch ( error_already_set const & ) {
//Here i can said that i have error, but i cant determine what caused an error
std::cout << "error!" << std::endl;
}
PyErr_Print() just prints error text to stderr and clears error so it can't be solution
回答1:
Well, I found out how to do it.
Without boost (only error message, because code to extract info from traceback is too heavy to post it here):
PyObject *ptype, *pvalue, *ptraceback;
PyErr_Fetch(&ptype, &pvalue, &ptraceback);
//pvalue contains error message
//ptraceback contains stack snapshot and many other information
//(see python traceback structure)
//Get error message
char *pStrErrorMessage = PyString_AsString(pvalue);
And BOOST version
try{
//some code that throws an error
}catch(error_already_set &){
PyObject *ptype, *pvalue, *ptraceback;
PyErr_Fetch(&ptype, &pvalue, &ptraceback);
handle<> hType(ptype);
object extype(hType);
handle<> hTraceback(ptraceback);
object traceback(hTraceback);
//Extract error message
string strErrorMessage = extract<string>(pvalue);
//Extract line number (top entry of call stack)
// if you want to extract another levels of call stack
// also process traceback.attr("tb_next") recurently
long lineno = extract<long> (traceback.attr("tb_lineno"));
string filename = extract<string>(traceback.attr("tb_frame").attr("f_code").attr("co_filename"));
string funcname = extract<string>(traceback.attr("tb_frame").attr("f_code").attr("co_name"));
... //cleanup here
回答2:
This is the most robust method I've been able to come up so far:
try {
...
}
catch (bp::error_already_set) {
if (PyErr_Occurred()) {
msg = handle_pyerror();
}
py_exception = true;
bp::handle_exception();
PyErr_Clear();
}
if (py_exception)
....
// decode a Python exception into a string
std::string handle_pyerror()
{
using namespace boost::python;
using namespace boost;
PyObject *exc,*val,*tb;
object formatted_list, formatted;
PyErr_Fetch(&exc,&val,&tb);
handle<> hexc(exc),hval(allow_null(val)),htb(allow_null(tb));
object traceback(import("traceback"));
if (!tb) {
object format_exception_only(traceback.attr("format_exception_only"));
formatted_list = format_exception_only(hexc,hval);
} else {
object format_exception(traceback.attr("format_exception"));
formatted_list = format_exception(hexc,hval,htb);
}
formatted = str("\n").join(formatted_list);
return extract<std::string>(formatted);
}
回答3:
In the Python C API, PyObject_Str returns a new reference to a Python string object with the string form of the Python object you're passing as the argument -- just like str(o)
in Python code. Note that the exception object does not have "information like line number" -- that's in the traceback object (you can use PyErr_Fetch to get both the exception object and the traceback object). Don't know what (if anything) Boost provides to make these specific C API functions easier to use, but, worst case, you could always resort to these functions as they are offered in the C API itself.
回答4:
This thread has been very useful for me, but I had problems with the Python C API when I tried to extract the error message itself with no traceback. I found plenty of ways to do that in Python, but I couldn't find any way to do this in C++. I finally came up with the following version, which uses the C API as little as possible and instead relies much more on boost python.
PyErr_Print();
using namespace boost::python;
exec("import traceback, sys", mainNamespace_);
auto pyErr = eval("str(sys.last_value)", mainNamespace_);
auto pyStackTrace = eval("'\\n'.join(traceback.format_exception(sys.last_type, sys.last_value, sys.last_traceback))", mainNamespace_);
stackTraceString_ = extract<std::string>(pyStackTrace);
errorSummary_ = extract<std::string>(pyErr);
The reason this works is because PyErr_Print() also sets the value for sys.last_value
, sys.last_type
, and sys.last_traceback
. Those are set to the same values as sys.exc_info
would give, so this is functionally similar to the following python code:
import traceback
import sys
try:
raise RuntimeError("This is a test")
except:
err_type = sys.exc_info()[0]
value = sys.exc_info()[1]
tb = sys.exc_info()[2]
stack_trace = "\n".join(traceback.format_exception(err_type, value, tb))
error_summary = str(value)
print(stack_trace)
print(error_summary)
I hope someone finds this useful!
来源:https://stackoverflow.com/questions/1418015/how-to-get-python-exception-text