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What is the problem or limitation you are having?

The stub app currently sets a PYTHONPATH that includes the app and app_packages paths, plus the stdlib.

These paths are all inside the application bundle, which the user may not have access to modify.

If a user wants to add additional files to the PYTHONPATH (e.g., if you were building a "Jupyter Notebook" app, and wanted the user to be able to access user-installed packages), you can't install that code into app or app_packages.

Describe the solution you'd like

The stub app should include an XDG compliant user path as part of the standard app path. This is probably:

~/.local/share/<app name>/user_packages

Describe alternatives you've considered

Don't allow user-installed packages.

Additional context

See beeware/briefcase-linux-appimage-template#30 and beeware/briefcase-linux-flatpak-template#18 for analogous problems.

Describe the bug

The stub binary used to start an app is an effective replacement for the python binary; however, it isn't a perfect replacements. multiprocessing in spawn mode will try to invoke sys.executable to spawn a child; it's also common to use subprocess or os.spawn to try and start sys.exectuable to run other Python code as a subprocess. However, the stub binary doesn't support this kind of execution.

Steps to reproduce

1. Generate a stub system app
2. Add a call to call multiprocessing.Process() and start it with .start()

The subprocess will call the parent process entry point, and fail.

Expected behavior

The function targeted by Process() should be invoked with the provided arguments.

Screenshots

No response

Environment

• Operating System: All Linux
• Python version: All
• Software versions:
  • Briefcase: 0.3.13

Logs

No response

Additional context

See beeware/briefcase-macOS-app-template#7 for an analogous report on macOS.

One possible solution would be to add some logic to the stub binary to inspect to see if the parent process is "self"; if so, the execution of the app should be modified to behave as if it were a normal Python binary.

Any solution should also be ported to macOS (beeware/briefcase-macOS-Xcode-template#20) and Windows (beeware/briefcase-windows-VisualStudio-template#8).