Re: Debugging of native extensions on windows

Hi Rokas

The typical solution (which I myself use frequently) is to enable your 
debugger to attach to child processes automatically. It can make things 
a bit noisier, but it's generally manageable, especially if you've got 
breakpoints set in your own code.

Another option is to not use the virtual environment, but set PYTHONPATH 
to your environment's Lib\site-packages directory and then run the base 
interpreter directly. Most of the time, this will be identical, but it 
avoids the extra process.

Unfortunately, for a variety of reasons, we can't get away from the 
redirector process as long as virtual environments keep their current 
design. As changing the design would be just as disruptive, we've not 
done anything yet, nor do we have any plans to change anything.

Finally, most discussion about Python occurs at 
https://discuss.python.org/ these days. You'll likely find more help and 
discussion over there.

Cheers,
Steve

On 3/13/2023 3:25 PM, Rokas Kupstys wrote:
> Hello!
> 
> I am dropping this mail to bring up an issue which cost me three good 
> evenings of time. Now that i figured it out i believe it is quite a 
> serious usability problem.
> 
> Gist of the problem: i have some C++ code wrapped with SWIG, so a native 
> extension. As with all software - there was a bug. However, no matter 
> what i did - i could not debug it in a native debugger. I ran 
> ".venv/Scripts/python.exe script.py" in a native debugger and 
> breakpoints would not be hit, application would crash eventually. This 
> was especially confusing, because exact same setup worked just fine on 
> linux. I eventually stumbled on to process list showing 
> ".venv/Scripts/python.exe" having spawned a subprocess... Which led me 
> to "PC/launcher.c" which is what ".venv/Scripts/python.exe" really is. I 
> cant find much information about this behavior in documentation even 
> after the fact. All in all, this was quite confusing. So now every time 
> i want to debug a native extension i have to start a program and then 
> attach a debugger to it, instead of just hitting "Debug" button in IDE. 
> It gets worse if crash happens immediately, which means i have to resort 
> to things like adding a message box somewhere to block execution and 
> give me enough time to attach the debugger. It works in the end, but 
> user experience is really not great. But whats worse - this is such a 
> non-obvious behavior that many more people may trip on it and waste 
> their time. Documenting this behavior would be of little help too, as 
> there is no clear path from the issue to the documentation on the matter...
> 
> So there it is. I am sure it is the way it is for a good reason. 
> However, this is a very error-prone process which is likely to waste 
> people's time. So maybe this behavior could be reconsidered? Or maybe 
> there is a solution already, which escaped me?
>