What is the router like?

[louiesun]

I want to put a config file (config.json), but I can't read it with

with open("config.json', 'r') as f:

-->ERROR: file not found
The file in under the same dictionary of app.py.

what is the router like and how to read and write files?

[freakboy3742]

I'm not sure what you mean by "the router" - Briefcase doesn't have any concept of a router.

However, the problem you're hitting is well understood in Briefcase-packaged apps - it's an issue with the current working directory.

When you open("config.json"), you're not explicitly giving the location of a file - you're implicitly asking to open a file named config.json in your current working directory. When you're running Python from a command line, that location is obvious - it's the location where you started the interpreter. But in a packaged app, it's not as obvious - what is your current working directory when you double click on an icon? Briefcase will deliberately set the working directory to the user's home directory specifically to highlight bugs like this one.

The fix is to not be implicit - and provide a fully qualified path to the file. Don't open("config.json") - instead, open("/full/path/to/config.json").

Determining /full/path/to is the next problem - and the solution depends on what toolkit you're using.

__file__ can be used in any Python code to report the full file that the code is currently in. You can then use Pathlib to get the directory that contains the current python file with Path(__file__).parent; and then construct the path to the config file from that root.

If you're using Toga, a Toga app provides App.paths that gives you access to a range of useful filesystem roots (in Pathlib format) that you can use to construct a full path.

[louiesun]

thanks, it work.
my router means how the programme look for the file.