def __delete__(self, instance):
if instance:<EOL><INDENT>if self.column.can_delete:<EOL><INDENT>instance._values[self.column.column_name].delval()<EOL><DEDENT>else:<EOL><INDENT>raise AttributeError('<STR_LIT>'.format(self.column.column_name))<EOL><DEDENT><DEDENT>
Sets the column value to None, if possible