Multiple Apps

[JPHutchins]

I decided to convert a project to multiple apps in order to share some GUI base classes. It works great!

When it comes to the pyproject.toml, I found that I had to copy out all of the entries like [tool.briefcase.app.firstapp.linux.system.suse] and repeat them with [tool.briefcase.app.secondapp.linux.system.suse] etc. Is there anyway to avoid this repetition and declare that all of the apps have the same briefcase dependencies?

[freakboy3742]

If the dependency is common to all app on all platforms, you can include the requirement in the project-level requires setting (i.e. in [tool.briefcase])

If the dependency is linux specific, but shouldn't be used on macOS/Windows, there's no "across all apps, on linux" section where you can put a declaration. That might be worth exploring as a feature; the question would be the exact resolution order (i.e., do platform level declarations come before or after app level declarations?)

However, there is another option: you can use PEP508 install qualifiers in the app-level section. For example:

[tool.briefcase]
...
requires = [
    "pillow==9.3.0; sys_platform == 'linux'",
    "pillow==9.2.0; sys_platform == 'darwin'",
]

This would install Pillow 9.3.0 on Linux, but Pillow 9.2.0 on macOS. You can use any of the qualifiers here (so, for example, you can gate installation on the Python version to install a backwards compatibility shim like importlib_metadata).

The only complication with this is that sys.platform == 'linux' on Android as well (at least, it does until Python 3.13; as of Python 3.13, Android reports as sys.platform == "android"). But if you're not planning to target Android, that's not a concern, it's entirely safe to use.

[chenkianwee]

Hi I am trying to create a multi app project too. My main motivation for doing that is both apps share many functions I have written. I am hoping by putting them in a single project I can reference the same module for both apps. However, I am not sure where to put the shared library in the briefcase folder structure. I tried doing this:

Myapp
     |----- src
          |----- myapp1
          |----- myapp2
          |----- shared_libs
     |----- tests

In my code myapp1/app.py I tried importing shared libs as so

from ..shared_libs import myshared_libs

But I am getting this error when i run briefcase dev
'ImportError: attempted relative import beyond top-level package'

what is the correct way to share a module between two apps in a single project? Thanks

[freakboy3742]

The rules about sharing code aren't any different than they are for a "normal" Python app - and as with a normal Python app, the key is ensuring that the code is on your PYTHONPATH where you expect.

The example directory layout you've shown is entirely fine as an input - but that's the point - it's just the input. That's not necessarily how the directory looks when it's deployed at runtime.

By default, your app My App 1 will have a sources definition of sources = ["src/myapp1"] or similar. That means that the myapp1 folder will be copied into your production app. myapp2 and shared_libs won't be.

If you add shared_libs to your sources definition (sources = ["src/myapp1", "src/shared_libs"]), the shared_libs directory will also be copied into your final app - but there won't be a .. namespace to traverse. .. isn't traversing directories, it's traversing the Python namespace - and shared_libs is at the top of the Python namespace tree. There is no module "above" myapp1 - myapp1 is a "top-level package", available directly on your PYTHONPATH.

However - you could run from shared_libs import ... - because shared_libs is also at the top of the Python namespace tree.

I hope that clarifies things; let me know if you need any further clarification.

[chenkianwee]

Thanks so much! It worked! I included "src/shared_libs" as one of my sources in the pyproject.toml file. Now I can import the library in my app.

[chenkianwee]

Might be useful for others who might be looking for managing multiple apps projects. This is how I setup testing for my different apps, will be good to hear if this is the recommended practice.

    proj_folder
        |--- src
        |--- tests
            |--- app1
                |--- test_app.py
            |--- app2
                |--- test_app.py
            |--- app1.py
            |--- app2.py

In the tests/app1.py file I have put in these codes to direct pytest to look into the tests/app1/ folder for test. Repeat this for app2 so you can write different test for each different app.

    args = sys.argv[1:]
    if len(args) == 0:
        args = ["tests/app1"]

Then you can run briefcase to test your app with the following command

briefcase run --test --app app1
briefcase run --test --app app2

[freakboy3742]

Yup - that's about what I'd expect to see in a multi-app setup.