在Python中,可以不使用继承来实现MIXIN行为吗?

def mixer(*args):
    """Decorator for mixing mixins"""
    def inner(cls):
        for a,k in ((a,k) for a in args for k,v in vars(a).items() if callable(v)):
            setattr(cls, k, getattr(a, k).im_func)
        return cls
    return inner

class Mixin(object):
    def b(self): print "b()"
    def c(self): print "c()"

class Mixin2(object):
    def d(self): print "d()"
    def e(self): print "e()"


@mixer(Mixin, Mixin2)
class Foo(object):
    # Somehow mix in the behavior of the Mixin class,
    # so that all of the methods below will run and
    # the issubclass() test will be False.

    def a(self): print "a()"

f = Foo()
f.a()
f.b()
f.c()
f.d()
f.e()
print issubclass(Foo, Mixin)

输出:

a()
b()
c()
d()
e()
False

可以将方法添加为函数:

Foo.b = Mixin.b.im_func
Foo.c = Mixin.c.im_func

我对Python不是很熟悉,但是根据我对Python元编程的了解,您实际上可以像在Ruby中那样做。

在Ruby中,模块基本上由两部分组成:指向方法字典的指针和指向常量字典的指针。类由三部分组成:指向方法字典的指针、指向常量字典的指针和指向超类的指针。

M 进了一个班 C

1. 匿名班 α 包含类 )
2. 的方法字典和常量字典指针设置为 的
3. ± 的超类指针设置为 的
4. 的超类指针设置为 ±

换言之:将一个与MIXIN共享行为的伪类注入到继承层次结构中。所以,鲁比实际上 使用遗传算法合成混合蛋白。

我省略了上面的几个转租:首先,模块实际上并没有作为 C类 C类 “s超类”(即 C类 的单例类)超类。其次,如果Mixin本身在其他混音中混合,那么 也被包装成假类,直接插入到上面 ±

基本上,整个MIXIN层次结构扁平化为直线,并拼接成继承链。

实际上,Python允许您在事实发生之后更改类的超类(Ruby做的事情 不 dict (同样,这在Ruby中是不可能的),所以您应该能够自己实现它。

编辑:修复了可能(也可能应该)被解释为bug的问题。现在,它构建了一个新的DICT,然后从类的DICT中更新它。这样可以防止MIXIN改写直接在类上定义的方法。 代码还未测试,但应该可以工作。我正忙着用自动取款机,所以我稍后再测试。 除了语法错误之外,它工作得很好。回想起来,我觉得我不喜欢它(即使在我进一步改进之后),我更喜欢它 my other solution 即使事情更复杂。这个测试代码也适用于这里,但我不会复制它。

 import inspect

 def add_mixins(*mixins):
     Dummy = type('Dummy', mixins, {})
     d = {}

     for mixin in reversed(inspect.getmro(Dummy)):
         d.update(mixin.__dict__)

     class WithMixins(type):
         def __new__(meta, classname, bases, classdict):
             d.update(classdict)
             return super(WithMixins, meta).__new__(meta, classname, bases, d)
     return WithMixins 

然后像这样使用它:

 class Foo(object):
     __metaclass__ = add_mixins(Mixin1, Mixin2)

     # rest of the stuff

explained by Jörg W Mittag . 所有的密码墙 if __name__=='__main__' 是测试/演示代码。实际上只有13行真正的代码。

import inspect

def add_mixins(*mixins):
    Dummy = type('Dummy', mixins, {})
    d = {}

    # Now get all the class attributes. Use reversed so that conflicts
    # are resolved with the proper priority. This rules out the possibility
    # of the mixins calling methods from their base classes that get overridden
    # using super but is necessary for the subclass check to fail. If that wasn't a
    # requirement, we would just use Dummy above (or use MI directly and
    # forget all the metaclass stuff).

    for base in reversed(inspect.getmro(Dummy)):
        d.update(base.__dict__)

    # Create the mixin class. This should be equivalent to creating the
    # anonymous class in Ruby.
    Mixin = type('Mixin', (object,), d)

    class WithMixins(type):
        def __new__(meta, classname, bases, classdict):
            # The check below prevents an inheritance cycle from forming which
            # leads to a TypeError when trying to inherit from the resulting
            # class.
            if not any(issubclass(base, Mixin) for base in bases):
                # This should be the the equivalent of setting the superclass 
                # pointers in Ruby.
                bases = (Mixin,) + bases
            return super(WithMixins, meta).__new__(meta, classname, bases,
                                                   classdict)

    return WithMixins 


if __name__ == '__main__':

    class Mixin1(object):
        def b(self): print "b()"
        def c(self): print "c()"

    class Mixin2(object):
        def d(self): print "d()"
        def e(self): print "e()"

    class Mixin3Base(object):
        def f(self): print "f()"

    class Mixin3(Mixin3Base): pass

    class Foo(object):
        __metaclass__ = add_mixins(Mixin1, Mixin2, Mixin3)

        def a(self): print "a()"

    class Bar(Foo):
        def f(self): print "Bar.f()"

    def test_class(cls):
        print "Testing {0}".format(cls.__name__)
        f = cls()
        f.a()
        f.b()
        f.c()
        f.d()
        f.e()
        f.f()
        print (issubclass(cls, Mixin1) or 
               issubclass(cls, Mixin2) or
               issubclass(cls, Mixin3))

    test_class(Foo)
    test_class(Bar)

你可以装饰课堂 __getattr__ 检查MIXIN。问题是,MIXIN的所有方法总是需要一个对象,即Mixin的类型作为它们的第一个参数,所以你必须进行装饰。 __init__ 同时创建一个MIXIN对象。我相信你可以用 class decorator .

from functools import partial
class Mixin(object):
    @staticmethod
    def b(self): print "b()"
    @staticmethod
    def c(self): print "c()"

class Foo(object):
    def __init__(self, mixin_cls):
        self.delegate_cls = mixin_cls

    def __getattr__(self, attr):
        if hasattr(self.delegate_cls, attr):
            return partial(getattr(self.delegate_cls, attr), self)

    def a(self): print "a()"

f = Foo(Mixin)
f.a()
f.b()
f.c()
print issubclass(Foo, Mixin)

这基本上使用 Mixin 分类为要保存的容器 通过将对象实例(self)作为第一个参数,其行为类似于方法的函数(而不是方法)。 __getattr__

这通过了如下所示的简单测试。但我不能保证它会做你想做的一切。做更彻底的测试来确定。

$ python mixin.py 
a()
b()
c()
False

例如,如果我想要 init_covers

import cove as cov


def init_covers(n):
    n.covers.append(cov.Cover((set([n.id]))))
    id_list = []
    for a in n.neighbors:
        id_list.append(a.id)
    n.covers.append(cov.Cover((set(id_list))))

def update_degree(n):
    for a in n.covers:
        a.degree = 0
        for b in n.covers:
            if  a != b:
                a.degree += len(a.node_list.intersection(b.node_list))    

在我的酒吧类文件中,我会做: import bedg as foo

如果我想在继承了bar的另一个类中更改foo行为,我会编写

import bild as foo

就像我说的,它很邋遢。