I am importing an abc file like so:
But I want to then get what I have imported and do stuff with it. I dont know whats in the file in advance - how can I find out what nodes I have just imported?
Right after you perform the import alembic operation, all the objects that are imported are selected in the viewport. So you can use the following code to get access to them
Then you can perform operations such as grouping them logically as below
Additionally, you also have access to cache files
Assuming you have loaded an alembic file (test2.abc) containing a cube and sphere, you can get to their object paths using
cache_file = bpy.data.cache_files['test2.abc']
Now we can get access to all the objects paths loaded