如何利用Mixin对已定义的类进行方法和属性扩展
###起因
类已经定义明确，但希望在创建实例时拓展实例的功能，这种情况下怎么办？
###目的
实现一种机制，能够根据一定的规则，在实例创建时动态的拓展实例的功能（方法和属性)；
###实现
- 动态的拓展类的方法和属性，这样所有实例都具备相应功能；
a. 利用python的动态特性：类也是对象，可以在运行时动态的创建它们，就像其他任何 对象一样；
b. 元类就是用来创建类的“东西”;
- Python会在内存中通过_metaclass_ = Foo 创建一个名字为Foo的类对象（我说的是类对象，请紧跟我的思路）,Python没有找到_metaclass_，它会继续在父类中寻找__metaclass__属性，并尝试做和前面同样的操作。如果Python在任何父类中都找不到__metaclass__，它就会在模块层次中去寻找_metaclass_，并尝试做同样的操作。如果还是找不到_metaclass_,Python就会用内置的type来创建这个类对象。
c.代码实现
class _MetaMixin(type): ''' 利用元编程扩展类属性和方法，示例： class DemoMixin1(object): __mixinname__ = 'DemoMixin' __metaclass__ = _MetaMixin def __init__(self): pass 这样即可将__mixinset__中收集到的__mixinname__相关的方法和属性扩展到自定义类中 自定义的类中必须包含如下两个类属性： __mixinname__ = 'DemoMixin' __metaclass__ = _MetaMixin ''' def __new__(cls, clsname, clsbases, clsdict): t = type.__new__(cls, clsname, clsbases, clsdict) mixinId = clsdict['__mixinname__'] if mixinId in __mixinset__: clsdict['__mixins__'] = __mixinset__[mixinId] for k, v in clsdict['__mixins__'].items(): clsdict[k] = v t = type.__new__(cls, clsname, clsbases, clsdict) return t**d.**使用举例：
class DemoMixin(object): __mixinname__ = 'DemoMixin' __metaclass__ = _MetaMixin def __init__(self): pass + **只须定义\__mixinname__和\__metaclass__** + \__mixinname__:__从\__mixinset\__中获取与自己相关的方法和属性__ + \__metaclass__：__在元类中根据\__mixinname\__拓展类的方法和属性__
2.动态的拓展实例的方法和属性；
a. 利用python的动态特性,在__init__对实例的__dict__进行动态扩展
b. 代码实现
class Mixin(object): __mixinname__ = '' #mixin interface name, all subclass need define its own __mixinname__ def __init__(self): self.initmixin() def initmixin(self): ''' 1. Add every item in __mixinset__[self.__mixinname__] into instance of the class which inherit from Mixin 2. Marked by class attr __mixinname__, all subclass need define its own __mixinname__ 为继承自Mixin的子类扩展__mixinset__[self.__mixinname__]中收集到的类和方法 __mixinset__为一字典，收集扩展方法和属性集合 __mixinname__为ID，标识旗下的方法和属性属于哪一个类 这种方法必须在子类中定义__mixinname__ ''' if self.__class__.__name__ == 'Mixin': #don't dealing Mixin class itself return if not self.__mixinname__: return if self.__mixinname__ in __mixinset__: self.__dict__.update(__mixinset__[self.__mixinname__]) setattr(self, '__mixins__', __mixinset__[self.__mixinname__]) def initmixin2(self): ''' if you use this method Marked by class attr __name__, all subclass don't need define its own __mixinname__ 直接以__name__为ID,不需要定义__mixinname__,但必须保证__mixinset__与类一一对应 ''' name = self.__class__.__name__ if name == 'Mixin': #don't dealing Mixin class itself return if name in __mixinset__: self.__dict__.update(__mixinset__[name]) setattr(self, '__mixins__', __mixinset__[name])**c.**使用说明
class DemoMixin(Mixin): __mixinname__ = 'DemoMixin' def __init__(self): self.initmixin()- 必须定义_mixinname_, 然后在__init__执行self.initmixin()
###如何收集需要拓展的属性和方法
**a.**利用全局变量_mixinset__收集所有需要拓展类的方法和属性，_mixinset 以__mixinname__为key,以相应属性和方法为value的字典形式存在
**b.**代码实现
__mixinset__ = {} # 收集所有需要扩展的类方法和属性 def setMixin(mixinname, name, value): ''' mixinname----ID name -----属性或方法名字 value-----对应属性或方法的具体实现 如果value为字典，则update更新相应的字典 如果value为列表，则extend拓展相应的列表 如果value为元组，则sum增加相应的元组 ''' if mixinname in __mixinset__: mixins = __mixinset__[mixinname] else: __mixinset__[mixinname] = {} mixins = __mixinset__[mixinname] if name in mixins: if isinstance(mixins[name], (dict, tuple, list)) and isinstance(value, (dict, tuple, list)): if isinstance(mixins[name], dict) and isinstance(value, dict): mixins[name].update(value) elif isinstance(mixins[name], list) and isinstance(value, list): mixins[name].extend(value) elif isinstance(mixins[name], tuple) and isinstance(value, tuple): mixins[name] = mixins[name] + value else: mixins[name] = value else: mixins[name] = valuec. 使用举例
收集属性和方法
def add(a, b): return a + b setMixin('DemoMixin', '1', 'aaaaaaaa') setMixin('DemoMixin', '2', (1,2,4)) setMixin('DemoMixin', '2', (3,4)) setMixin('DemoMixin', '6', [1, 2, 3]) setMixin('DemoMixin', '6', [7, 8, 9]) setMixin('DemoMixin', '3', {1:2}) setMixin('DemoMixin', '3', {1:3}) setMixin('DemoMixin', '5', 'asssssssssssssssssssssssssss') setMixin('DemoMixin', '5', (1,2,3,45)) setMixin('DemoMixin', '5', 'assss') setMixin('DemoMixin', '5', [1,2]) setMixin('DemoMixin', 'add', add) import os setMixin('DemoMixin', 'getcwd111', os.getcwd)
###测试Demo演示：
**a.**测试代码
class DemoMixin1(object): __mixinname__ = 'DemoMixin' __metaclass__ = _MetaMixin def __init__(self): pass class DemoMixin2(Mixin): __mixinname__ = 'DemoMixin' def __init__(self): self.initmixin() def main(): d1 = DemoMixin1() print dir(DemoMixin1) print DemoMixin1.__dict__ print dir(d1) print d1.__dict__ print '-' * 20 d2 = DemoMixin2() print dir(DemoMixin2) print DemoMixin2.__dict__ print dir(d2) print d2.__dict__ if __name__ == '__main__': main()- 测试结果过大，不做显示，自己可以运行下面的完整demo程序查看结果
**b.**完整代码Demo
#!/usr/bin/python # -*- coding: utf-8 -*- ''' 目的：当实例创建时，根据收集到的配置对相应的类进行动态方法和属性扩展 方式有两种： 第一种：直接扩展类属性和方法，这种方式使用元编程__new__实现较好； 直接拓展类clsdict，因为clsdict中存放的即为所有类属性和方法的集合 第二种：直接扩展实例属性和方法，这种方式在初始化__init__中实现较好； 直接拓展实例__dict__,因为__dict__中存放的即为所有实例属性和方法的集合 ''' __mixinset__ = {} # 收集所有需要扩展的类方法和属性 class Object_Dict(dict): ''' Makes a dictionary behave like an object. ''' def __init__(self, *args, **kw): dict.__init__(self, *args, **kw) self.__dict__ = self class _MetaMixin(type): ''' 利用元编程扩展类属性和方法，示例： class DemoMixin1(object): __mixinname__ = 'DemoMixin' __metaclass__ = _MetaMixin def __init__(self): pass 这样即可将__mixinset__中收集到的__mixinname__相关的方法和属性扩展到自定义类中 自定义的类中必须包含如下两个类属性： __mixinname__ = 'DemoMixin' __metaclass__ = _MetaMixin ''' def __new__(cls, clsname, clsbases, clsdict): t = type.__new__(cls, clsname, clsbases, clsdict) mixinId = clsdict['__mixinname__'] if mixinId in __mixinset__: clsdict['__mixins__'] = __mixinset__[mixinId] for k, v in clsdict['__mixins__'].items(): clsdict[k] = v t = type.__new__(cls, clsname, clsbases, clsdict) return t class Mixin(object): __mixinname__ = '' #mixin interface name, all subclass need define its own __mixinname__ def __init__(self): self.initmixin() def initmixin(self): ''' 1. Add every item in __mixinset__[self.__mixinname__] into instance of the class which inherit from Mixin 2. Marked by class attr __mixinname__, all subclass need define its own __mixinname__ 为继承自Mixin的子类扩展__mixinset__[self.__mixinname__]中收集到的类和方法 __mixinset__为一字典，收集扩展方法和属性集合 __mixinname__为ID，标识旗下的方法和属性属于哪一个类 这种方法必须在子类中定义__mixinname__ ''' if self.__class__.__name__ == 'Mixin': #don't dealing Mixin class itself return if not self.__mixinname__: return if self.__mixinname__ in __mixinset__: self.__dict__.update(__mixinset__[self.__mixinname__]) setattr(self, '__mixins__', __mixinset__[self.__mixinname__]) def initmixin2(self): ''' if you use this method Marked by class attr __name__, all subclass don't need define its own __mixinname__ 直接以__name__为ID,不需要定义__mixinname__,但必须保证__mixinset__与类一一对应 ''' name = self.__class__.__name__ if name == 'Mixin': #don't dealing Mixin class itself return if name in __mixinset__: self.__dict__.update(__mixinset__[name]) setattr(self, '__mixins__', __mixinset__[name]) def setMixin(mixinname, name, value): ''' mixinname----ID name -----属性或方法名字 value-----对应属性或方法的具体实现 如果value为字典，则update更新相应的字典 如果value为列表，则extend拓展相应的列表 如果value为元组，则sum增加相应的元组 ''' if mixinname in __mixinset__: mixins = __mixinset__[mixinname] else: __mixinset__[mixinname] = {} mixins = __mixinset__[mixinname] if name in mixins: if isinstance(mixins[name], (dict, tuple, list)) and isinstance(value, (dict, tuple, list)): if isinstance(mixins[name], dict) and isinstance(value, dict): mixins[name].update(value) elif isinstance(mixins[name], list) and isinstance(value, list): mixins[name].extend(value) elif isinstance(mixins[name], tuple) and isinstance(value, tuple): mixins[name] = mixins[name] + value else: mixins[name] = value else: mixins[name] = value def add(a, b): return a + b setMixin('DemoMixin', '1', 'aaaaaaaa') setMixin('DemoMixin', '2', (1,2,4)) setMixin('DemoMixin', '2', (3,4)) setMixin('DemoMixin', '6', [1, 2, 3]) setMixin('DemoMixin', '6', [7, 8, 9]) setMixin('DemoMixin', '3', {1:2}) setMixin('DemoMixin', '3', {1:3}) setMixin('DemoMixin', '5', 'asssssssssssssssssssssssssss') setMixin('DemoMixin', '5', (1,2,3,45)) setMixin('DemoMixin', '5', 'assss') setMixin('DemoMixin', '5', [1,2]) setMixin('DemoMixin', 'add', add) import os setMixin('DemoMixin', 'getcwd111', os.getcwd) class DemoMixin1(object): __mixinname__ = 'DemoMixin' __metaclass__ = _MetaMixin def __init__(self): pass class DemoMixin2(Mixin): __mixinname__ = 'DemoMixin' def __init__(self): self.initmixin() def main(): d1 = DemoMixin1() print dir(DemoMixin1) print DemoMixin1.__dict__ print dir(d1) print d1.__dict__ print '-' * 20 d2 = DemoMixin2() print dir(DemoMixin2) print DemoMixin2.__dict__ print dir(d2) print d2.__dict__ if __name__ == '__main__': main()
