Get file source through python, not from disk

[timkpaine]

If I'm looking correctly, this line of code makes the assumption that the file's source is on disk: https://github.com/jupyter-xeus/xeus-python/blob/master/src/xdebugger.cpp#L216

However, it is quite easy to configure Python to allow files to be imported from e.g. network/remote. So maybe it would make sense to failover, if the file does not exist on disk then instead attempt to read source from the python object e.g. inspect.getsource.

[martinRenou]

Makes sense, although I am not sure we can rely on Python in this part of the code, there is no Python interpreter running here. What do you think @JohanMabille?

[JohanMabille]

There are two ways to get Python code executed from xdebugger.cpp:

• either send the code to the shell through the control_messenger object, as done here. The problem here is that the source is usually asked after the execution flow hits a breakpoint, therefore you cannot get the Python interpreter execute any code before you resume the execution.

• send an Evaluate request to PTVSD. However, I'm pretty sure this requires the interpreter to be stopped on a breakpoint. Even if I don't see any use case that asks for a source while the code is executing, we should hande this case too.

So the solution would be to use one of this solution depending on the interpreter state.