Returning an error instead of raising it

[ghlecl]

Hi.

In some python programming I do, I find it useful to return an error instead of raising it. Thus, I sometimes do:

def fn_a( some_param ):
   # do something with parameter
   if some_bad_condition:
      return ValueError( "this is why" )

def fn_b( params_again ):
   res = fn_a( params_again )
   if isinstance( res, Exception ):
      do something
   # rest of code

Whether or not this is a bad practice (it might very well be considered bad practice), I was trying to port some of my code to pybind11, but I could not instantiate an error and return it. Since pybind11::value_error is a C++ error, when you return it to python, it rightfully complains that it got an object it doesn't know what to do with.

I have looked into creating an object directly with the C API, but from my understanding after a few hours of looking at the python doc, reading on the C API and reading stack overflow answers, it does not seem straight forward without raising the exception (and I might/"hope to" be wrong).

Is something like that possible with pybind ? Could someone point me in the right direction ?

PS: This is my first steps with pybind11 and I want to congratulate anyone involved with it: I find it incredibly well done and the documentation very helpful. So thanks and congrats if you are reading this and are a contributor.

[ghlecl]

I have found a way via pybind. I am just uncertain of the performance penalty if any that it incurs.

Here is the solution I have found:

auto some_fn {
   py::object ValueError = py::module_::import("builtins").attr("ValueError");
   auto err = ValueError( "blablabla" );
   return err;
}

Does that internally call the C API, or does it run the interpreter ? I am still trying to figure all this out. Sorry if the questions are a bit basic.