def __delitem__(self, key):
        """Remove a flexible attribute from the model.
        """
        if key in self._values_flex:  # Flexible.
            del self._values_flex[key]
            self._dirty.add(key)  # Mark for dropping on store.
        elif key in self._getters():  # Computed.
            raise KeyError(u'computed field {0} cannot be deleted'.format(key))
        elif self._fields in key:  # Fixed.
            raise KeyError(u'fixed field {0} cannot be deleted'.format(key))
        else:
            raise KeyError(u'no such field {0}'.format(key))
dataset/ETHPy150Open beetbox/beets/beets/dbcore/db.py/Model.__delitem__/swapped operands of `in`