Python：如何在对象列表上链接方法？

Question

我希望能够在具有子节点和孙节点的节点实例上链接方法。当我在该顶部节点上调用方法时，我希望能够返回该对象的子孙。我还希望能够从最顶层节点获取这些子孙的属性。我有以下数据模型：

class GrandParent(object):
    def __init__(self,name='',age=0,is_retired=True,children=[]):
        self.name = name
        self.age = age
        self.is_retired = is_retired

        if children:
            self.children = children

    def print_mychildren(self):
       for child in self.children:
            print "Child: ",child

    def mychildren(self):
        return self.children

    def __str__(self):
        return "name: %s age: %s is_retired:%s" %(self.name,self.age,self.is_retired)


class Parent(object):
    def __init__(self,name='',age=0,has_mortgage=True,children=[]):
        self.name = name
        self.age = age
        self.has_mortgage = has_mortgage

        if children:
            self.children = children

    def print_mychildren(self):
       for child in self.children:
            print "Child: ",child

    def __str__(self):
        return "name: %s age: %s has_mortgage: %s" %(self.name,self.age,self.has_mortgage)


class Child(object):
    def __init__(self,name='',age=0,has_toys=True):

        self.name = name
        self.age = age
        self.has_toys = has_toys

    def __str__(self):
        return "name: %s age: %s has_toys:%s" %(self.name,self.age,self.has_toys)



if __name__ == '__main__':

    beaver = Child('Beaver',12,True)
    ward = Child('Ward',16,False)

    june = Parent('June',38,True,[beaver,ward])

    grandpa = GrandParent('Grandpa',61,True,[june])

    print grandpa

    grandpa.print_mychildren() # print June

    # Doesn't work
    grandpa.mychildren().print_mychildren() #  I want it to print Ward and Beaver
    # Doesn't work
    print grandpa.mychildren().mychild('Beaver').age # I want it to return an age

请注意，我想将 GrandParent、Parent 和 Child 类分开，因为我想为每个类赋予不同的属性，例如 has_mortgage 或 is_retired。

从上面的数据模型中，我希望能够链接方法以遍历顶部节点的子节点。它看起来像这样：

grandpa.children # returns a list of children
print grandpa.mychild('June').has_mortgage # returns the value
grandpa.mychildren().mychildren() # prints a list of grandchildren
print grandpa.mychildren().mychild('Ward').has_toys # return the value

换句话说，我可以发表声明吗：

print grandpa.mychildren().mychildren()

表现得像：

for child in grandpa.children:
        for grandchild in child.children:
            print grandchild

非常感谢您对此的回答。谢谢。

保罗
伊利诺伊州芝加哥

Answer 1

你可以做你想做的事，但这需要一些工作。您需要将您的Parent 和Grandparent 类的children 值设为自定义容器，以便将对方法和成员变量的访问映射到其内容。

这是一个可能的实现。它可能有一些我没有整理出来的奇怪的极端情况，但它适用于我尝试过的基本内容：

from operator import attrgetter

class mappingContainer(object):
    def __init__(self, contents):
        self.contents = contents

    # sequence protocol methods    
    def __getitem__(self, index):
        return self.contents[index]

    def __setitem__(self, index, value):
        self.contents[index] = value

    def __iter__(self):
        return iter(self.contents)

    def __contains__(self, o):
        return o in self.contents

    def __len__(self):
        return len(self.contents)

    # map attribute access and method calls
    def __getattr__(self, name):
        return mappingContainer(map(attrgetter(name), self.contents))

    def __call__(self, *args, **kwargs):
        return mappingContainer([o(*args, **kwargs) for o in self.contents])

    # string conversions
    def __repr__(self):
        return "mappingContainer(%s)" % repr(self.contents)

这是一个简单的“Person”类，我用来测试它。每个人都有一个名字，mappingContainer 中有零个或多个孩子，以及一个任意命名的方法，该方法打印一些内容并返回一个值。

class Person(object):
    def __init__(self, name, children = None):
        self.name = name
        if not children:
            children = []
        self.children = mappingContainer(children)

    def __repr__(self):
        return self.name

    def someMethod(self):
        print "%s's someMethod()" % str(self)
        return "%s's return value" % str(self)

这是我测试它的方法（用长线包裹，在这里展示）：

>>> c1 = Person("Adam")
>>> c2 = Person("Albert")
>>> c3 = Person("Alice")
>>> c4 = Person("Agnes")
>>> p1 = Person("Bob", [c1, c2])
>>> p2 = Person("Betty", [c3,c4])
>>> gp = Person("Charles", [p1, p2])
>>> gp
Charles
>>> gp.children
mappingContainer([Bob, Betty])
>>> gp.children.children
mappingContainer([mappingContainer([Adam, Albert]),
                  mappingContainer([Alice, Agnes])])
>>> gp.children.children.someMethod()
Adam's someMethod()
Albert's someMethod()
Alice's someMethod()
Agnes's someMethod()
mappingContainer([mappingContainer(["Adam's return value",
                                    "Albert's return value"]),
                  mappingContainer(["Alice's return value",
                                    "Agnes's return value"])])

现在这可能不是您想要的，因为您不能通过gp.children.children 直接迭代孙子（虽然函数调用会一直冒泡，但它们的结果仍将嵌套在两层容器中)。我认为 mappingContainer 可能会以某种方式进行调整来解决这个问题，但我不确定它是否值得。

如果出现任何问题，这种链式调用将成为调试的噩梦（除非您是超人，否则代码中的某些内容总会在开发的某个阶段出错）。如果您明确地迭代或递归您拥有的关系层次结构，您的代码将更容易编写和理解。

Answer 2

一种方法是为列表集合创建一个包装器（有点类似于 jQuery 处理方法链的方式）

代码：

class ChainList(list):
    def __getattribute__(self, name):
        try:
            return object.__getattribute__(self, name)
        except:
            pass

        return ChainList([getattr(child, name) 
            for child in self if name in dir(child)])

    def __call__(self, *args, **kwargs):       
        return ChainList([child(*args, **kwargs)
            for child in self if callable(child)])

class GrandParent(object):
    def __init__(self,name='',age=0,is_retired=True,children=[]):
        self.name = name
        self.age = age
        self.is_retired = is_retired

        if children:
            self.children = ChainList(children)

    def print_mychildren(self):
       for child in self.children:
            print "Child: ",child

    def mychildren(self):
        return self.children

    def __str__(self):
        return "name: %s age: %s is_retired:%s" %(self.name,self.age,self.is_retired)

class Parent(object):
    def __init__(self,name='',age=0,has_mortgage=True,children=[]):
        self.name = name
        self.age = age
        self.has_mortgage = has_mortgage

        if children:
            self.children = ChainList(children)

    def print_mychildren(self):
       for child in self.children:
            print "Child: ",child

    def __str__(self):
        return "name: %s age: %s has_mortgage: %s" %(self.name,self.age,self.has_mortgage)

    def mychild(self, name):
        for child in self.children:
            if child.name == name:
                return child

class Child(object):
    def __init__(self,name='',age=0,has_toys=True):

        self.name = name
        self.age = age
        self.has_toys = has_toys

    def __str__(self):
        return "name: %s age: %s has_toys:%s" %(self.name,self.age,self.has_toys)



if __name__ == '__main__':

    beaver = Child('Beaver',12,True)
    ward = Child('Ward',16,False)

    june = Parent('June',38,True,[beaver,ward])

    grandpa = GrandParent('Grandpa',61,True,[june])

    print grandpa

    grandpa.print_mychildren() # print June

    # Doesn't work
    grandpa.mychildren().print_mychildren() #  I want it to print Ward and Beaver
    # Doesn't work
    print grandpa.mychildren().mychild('Beaver').age # I want it to return an age

主要思想是 ChainList 类并覆盖 __getattribute__ 和 __call__ 并包装所有需要与此类链接的列表。

我还将 mychild() 添加到 Parent 以使示例正常运行。

Answer 3

对我来说，这听起来很像您在谈论模型和模型关系。看看 Django。 Django Models 会做你想做的事，你可以定义模型和query across those relations 之间的关系。