Get information of a certain quantity.
        If *key* is `None`, return the full dict for that quantity.

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

        if key is None:
            return d

        return d.get(key, default)