The system-files interface is used to access files from the host file-system, outside of the user’s home directory, which are not normally exposed to snaps. As such when using this interface, a snap needs to explicitly list which files / paths it requires access to.
However, currently pyflow simply plugs system-files but does not list access to any particular files. You need to list which files / paths are required and what access is required to these (read/write) as per the documentation when plugging this interface - so please update your snapcraft.yaml with specific paths, and then mention in this request post why access to those paths is required so that the review can take place.
I need it to be able to access whatever directory has Python installed to, or the user needs to run pyflow in. Perhaps classic would be more appropriate.
Yes classic might be more appropriate - can you please detail in your original thread what exactly pyflow requires access to and how it makes use of that from the host system and hence why classic confinement is appropriate?