finder.py

from importlib.machinery import ModuleSpec

class DataPackageFinder:
    """
    Data package module loader finder. This class sits on `sys.meta_path` and returns the
    loader it knows for a given path, if it knows a compatible loader.
    """

    @classmethod
    def find_spec(cls, fullname, path=None, target=None):
        """
        This functions is what gets executed by the loader.
        """
        name_parts = fullname.split('.')
        if name_parts[:2] != ['t4', 'data'] or len(name_parts) > 3:
            return None
        else:
            return ModuleSpec(fullname, DataPackageImporter())