Briefcase can't install Python packages with binary modules on mobile platforms.

Describe the bug

Briefcase is able to package any an app that has a dependency that is a pure-Python package (i.e., a package that contains only Python code).

However, if you’re targeting a mobile platform (iOS or Android), and the Python module has a binary component (i.e., it contains a C module), any attempt to import that module will fail, causing the app to crash.

Desktop platforms (macOS, Windows and Linux) are not affected by this problem.

To Reproduce Steps to reproduce the behavior:

1. Set up a hello world application
2. Add a package with a binary dependency (e.g., numpy or pillow) to the requires list, and add an import for that code (e.g., import numpy or import pil)
3. Deploy the app to iOS or Android
4. Try to run the app.

Expected behavior

The import should succeed and the app should continue to run.

Environment:

• Operating System: iOS or Android
• Python version: Any
• Software versions:
  • Briefcase: Any

Additional context

This isn’t purely a Briefcase issue; pip and PyPI doesn’t currently have any support for mobile platforms.

[renefritze]

Is this limitation mentioned in the docs? I’ve run through the tutorials and only saw the “platform notice”. An explicit note would have saved me a good chunk of time 😞

[eliteraspberries]

I modified the hello world tutorial like so:

        import numpy
        label = toga.Label(
            'Hello NumPy, {}'.format(numpy.random.random()),
            style=Pack(padding=(10, 10))
        )
        main_box.add(label)

and the result:

Pull request incoming…