I would have named this internal helpers differently: I would not use the underscore. Also, "get" can often seems a bit superfluous.
and for def _get_data(self):
For, the name _get_data was a bit confusing and was looking for what it actually returns. Perhaps a name such as _prepare_data or _load_data or similar would be more appropriate next time.
From orange-spectroscopy #262, Marko suggested:
For
def _get_prop_str(dat, param):
and for
def _get_data(self):