__file__ is not defined in 'sourced' Python scripts

[kevinushey]

For example, with the script:

print(__file__)

One can run the script in a standalone Python instance and see e.g.

$ python3 abc.py
/Users/kevin/scratch/abc.py

However, __file__ doesn't get defined for scripts sourced by reticulate:

> reticulate::source_python('~/scratch/abc.py')
Error in py_run_file_impl(file, local, convert) : 
  NameError: name '__file__' is not defined

Maybe py_run_file() should go through https://docs.python.org/3/c-api/veryhigh.html#c.PyRun_SimpleFile rather than https://docs.python.org/3/c-api/veryhigh.html#c.PyRun_StringFlags?

[kevinushey]

In case it's relevant:

https://github.com/python/cpython/blob/c5140945c723ae6c4b7ee81ff720ac8ea4b52cfd/Python/pythonrun.c#L392-L404

[t-kalinowski]

PyRun_SimpleFile unfortunately doesn't expose the locals and globals arguments, which we will need I think to maintain support for py_run_file(local = TRUE) usage.

PyRun_File does expose the globals and locals arguments, but it doesn't set __file__ and __cached__ for us. It looks like we'll have to do that manually. (PyRun_FileExFlags just reads compiles and goes straight to eval, with some error handling along the way. The only attr it ensures is __builtins__ if globals is main)

Something that's interesting is that in PyRun_SimpleFile, the __file__ item is deleted from the dictionary before returning. __file__ is only available during code execution. I think that makes sense if code is being evaluated in __main__, but I'm less sure if that's the correct behavior if we're evaluating in a local dict pseudo-module.