将属性添加到类列表以返回具有特定属性的所有对象

Question

我有以下问题：

让我们开始吧！

假设我有一个具有一些基本属性的类 Person：

class Person(object):
    def __init__(self, name=None, gender=None, single=None):
        self.name=name
        self.gender=gender
        self.single=single

我创建了一个名为 Dating 的列表类，它将包含所有 Person 对象

class Dating(object):
    def __init__(self):
        self.members=[]

My_People=Dating()

My_People.members.append(Person("Jack","Male",False))
My_People.members.append(Person("Jill","Female",True))
My_People.members.append(Person("George","Male",True))
My_People.members.append(Person("Sandy","Female",False))

对，那么问题出在哪里？

是否可以通过创建某种属性来为列表类分配一个属性以访问 My_People 列表的单个成员：

My_People.members.singles

这样会返回一个具有 single == True 属性的 Person 对象列表吗？

感谢所有帮助。 （顺便说一句，我以前对 Python 的经验很少）

Answer 1

如果您不受 My_People.members.singles 语法的约束，您可以更简单地执行此操作：

class Dating(object):

    def __init__(self):
        self.members = []

    @property
    def single_members(self):
        return [m for m in members if m.single]

现在您可以通过以下方式访问列表：

My_People.single_members

Answer 2

怎么样：

class Attribute(list):
    def __getattr__(self, attr):
        if attr == 'single':
            return [person for person in self if person.single]
        raise AttributeError()

class Person(object):
    def __init__(self, name=None, gender=None, single=None):
        self.name = name
        self.gender = gender
        self.single = single

    def __repr__(self):
        return 'Person({person.name}, {person.gender}, {person.single})'.format(person=self)


class Dating(object):
    members = Attribute()


My_People = Dating()

My_People.members.append(Person("Jack", "Male", False))
My_People.members.append(Person("Jill", "Female", True))
My_People.members.append(Person("George", "Male", True))
My_People.members.append(Person("Sandy", "Female", False))

>>> print My_People.members.single
[Person(Jill, Female, True), Person(George, Male, True)]
>>> print My_People.members
[Person(Jack, Male, False), Person(Jill, Female, True), Person(George, Male, True), Person(Sandy, Female, False)]

Answer 3

要添加这样的属性，您必须子类列表类型：

class FilterableList(list):
    def __getattr__(self, name):
        # assume non-existing attributes are boolean filters
        return [elem for elem in self if getattr(elem, name)]

请注意，这并不是那么灵活；只有True 值是通过这种方式找到的。您可以赋予属性名称更多含义，但通常无论如何您都希望在Dating 类上执行此操作，并使用方法更有表现力地过滤您的数据。

演示：

>>> class Person(object):
...     def __init__(self, name, gender, single):
...         self.name=name
...         self.gender=gender
...         self.single=single
...     def __repr__(self):
...         return 'Person({name!r}, {gender!r}, {single!r})'.format(**vars(self))
... 
>>> class FilterableList(list):
...     def __getattr__(self, name):
...         # assume non-existing attributes are boolean filters
...         return [elem for elem in self if getattr(elem, name)]
... 
>>> members = FilterableList([Person("Jack","Male",False), Person("Jill","Female",True), Person("George","Male",True), Person("Sandy","Female",False)])
>>> members
[Person('Jack', 'Male', False), Person('Jill', 'Female', True), Person('George', 'Male', True), Person('Sandy', 'Female', False)]
>>> members.single
[Person('Jill', 'Female', True), Person('George', 'Male', True)]

Answer 4

首先，您不需要在 My_People 实例上调用 __init__()，Python 会自动执行此操作。

对于这个问题，您可以从 list 继承并添加一个 singles 属性，如下所示：

class Person(object):
    def __init__(self, name=None, gender=None, single=None):
        self.name=name
        self.gender=gender
        self.single=single

class Dating(list):
    @property
    def singles(self):
        return [person for person in self if person.single ]

My_People=Dating()

My_People.append(Person("Jack","Male",False))
My_People.append(Person("Jill","Female",True))
My_People.append(Person("George","Male",True))
My_People.append(Person("Sandy","Female",False))

print My_People.singles