| # Copyright 2017 The Chromium Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| class SlotsMetaclass(type): |
| """This metaclass requires all subclasses to define __slots__. |
| |
| Usage: |
| class Foo(object): |
| __metaclass__ = slots_metaclass.SlotsMetaclass |
| __slots__ = '_property0', '_property1', |
| |
| __slots__ must be a tuple containing string names of all properties that the |
| class contains. |
| Defining __slots__ reduces memory usage, accelerates property access, and |
| prevents dynamically adding unlisted properties. |
| If you need to dynamically add unlisted properties to a class with this |
| metaclass, then take a step back and rethink your goals. If you really really |
| need to dynamically add unlisted properties to a class with this metaclass, |
| add '__dict__' to its __slots__. |
| """ |
| |
| def __new__(mcs, name, bases, attrs): |
| assert '__slots__' in attrs, 'Class "%s" must define __slots__' % name |
| assert isinstance(attrs['__slots__'], tuple), '__slots__ must be a tuple' |
| |
| return super(SlotsMetaclass, mcs).__new__(mcs, name, bases, attrs) |
