Question

class Square():
    def __init__(self, side):
        self.side = side

    def getArea(self):
        return side*side

    def getAreaOfAllInstances(self):
       {need to write this method}

s1 = Square(2)
s2 = Square(3)

print(s1.getAreaOfAllInstances()) ===> This should print 13 (2*2 + 3*3)
print(s2.getAreaOfAllInstances()) ===> This should print 13 (2*2 + 3*3)`

Answer 1

您可以使用类变量：

class Square():
    squares = []
    def __init__(self, side):
        self.side = side
        self.squares.append(self)

    def getArea(self):
        return self.side * self.side

    def getAreaOfAllInstances(self):
        return sum(s.getArea() for s in self.squares)

s1 = Square(2)
s2 = Square(3)

print(s1.getAreaOfAllInstances()) #===> This should print 13 (2*2 + 3*3)
print(s2.getAreaOfAllInstances()) # ===> This should print 13 (2*2 + 3*3)

但这不是一个干净的解决方案。我宁愿创建另一个类来跟踪Square。像这样：

class Square:
    def __init__(self, side):
        self.side = side

    def getArea(self):
        return self.side * self.side


class SquareContainer:
    def __init__(self):
        self.squares = []

    def create_square(self, side):
        square = Square(side)
        self.squares.append(square)
        return square

    def getAreaOfAllInstances(self):
        return sum(s.getArea() for s in self.squares)

sc = SquareContainer()
s1 = sc.create_square(2)
s2 = sc.create_square(3)

print(sc.getAreaOfAllInstances())

Answer 2

确定可以：

class Square():

    _all_instances = []

    def __init__(self, side):
        self.side = side
        self._all_instances.append(self)

    def getArea(self):
        return side*side

    @classmethod
    def getAreaOfAllInstances(cls):
        return sum(inst.getArea() for inst in cls._all_instances)

但是请注意，这意味着除非您清空Square属性，否则将永远不会收集Square._all_instances。

Answer 3

您可以使用类方法来实现这一目标。

<div id='nav'>
  <ul>
    <li>Item 1</li>
    <li>Item 2</li>
    <li>Item 3</li>
    <li>Item 4</li>
    <li>Item 5</li>
  </ul>
</div>

输出：

class Square(object):
    instances_list = []  # Property of the class

    def __init__(self, side):
        self.trackInstances(self)
        self.side = side

    def getArea(self):
        return self.side**2

    @classmethod
    def trackInstances(cls, self):
        self.instances_list.append(self)

    @classmethod
    def getAreaOfAllInstances(cls):
        areaSum = sum(map(lambda i: i.getArea(), cls.instances_list))
        print('square of all instances: {}'.format(areaSum))

s1 = Square(2)
s2 = Square(3)

s2.getAreaOfAllInstances()

请注意，只有square of all instances: 13被执行，它给出了所有实例的区域。

返回该类所有实例的另一个方法返回的值的总和？

3 个答案: