def get_quantity_info(self, quantity, key=None, default=None):
d = self._get_quantity_info_dict(quantity, default if key is None else dict())<EOL>if key is None:<EOL><INDENT>return d<EOL><DEDENT>return d.get(key, default)<EOL>
Get information of a certain quantity.
If *key* is `None`, return the full dict for that quantity.