Better error handling when root_folder is empty or lacks valid devices

[sametSeckiiin]

Hi,

I noticed that when initializing the Experiment class with a root_folder that is either empty or doesn't contain any valid device data, the library throws a ValueError that is a bit confusing for a first-time user:

ValueError: Experiment time range could not be determined: no devices with valid start_time and end_time were found.

This happens because _load_devices() expects to find data immediately to calculate the experiment's duration. However, this prevents creating an "empty" experiment object to which devices could potentially be added later programmatically.

It would be great if the library could either:

1-Provide a more descriptive error message (e.g., "The provided root_folder is empty or contains no valid device subfolders").

2Allow the initialization of an empty Experiment object (perhaps with an allow_empty=True flag) so we can add data later.

I'm happy to help with a PR if this is something you'd like to improve!

[pollytur]

Hi @sametSeckiiin and thanks for your interest in experanto

1 - for the error message - imho its fine enough “no devices with valid start_time and end_time were found.” is kinda same as and a bit more generic than the proposed “The provided root_folder is empty or contains no valid device subfolders”. The user sees that the error is with the device data and seeing that the folder is empty is relatively straighforward.

2 - I think empty folders is not a great idea as the experiment is supposed to be finished when experanto is used, so all data should be there before experanto. I don't see a usecase for having and Experiment wrapper on an empty folder to but maybe I’m missing sth

@schewskone @reneburghardt any opinions?