Question

我想维护A和B对象的计数，B是A的子类。所以计数应该特定于A和B.例如，如果我创建3个A对象和2个B对象，则由于构造函数呼叫，计数A变为3 + 2 = 5，但我想保持3（不作为B的一部分用作子对象）。请评论以下代码段：

class A:
    acount = 0 # class variable
    def __init__(self, isFullA = True):
        if (isFullA):
            self.iamFullA = True
            A.acount += 1
        else:
            self.iamFullA = False
    def __del__(self):
        if (self.iamFullA):
            A.acount -= 1

class B(A):
    bcount = 0 # class variable
    def __init__(self, isFullB = True):
        A.__init__(self,False)
        if (isFullB):
            self.iamFullB = True
            B.bcount += 1
        else:
            self.iamFullB = False
    def __del__(self):
        if (self.iamFullB):
            B.bcount -= 1
#MAIN
L=[]
for i in range(3):
  L.append(A())
for i in range(2):
  L.append(B())
print "A.acount = " + str(A.acount)
print "B.bcount = " + str(B.bcount)

输出结果为：

A.acount = 3
B.bcount = 2

Answer 1

您正在努力实现复杂化 - 您需要的是为每个类设置一个独特的count类属性：

class A(object):
    _counter = 0

    @classmethod
    def _inc(cls):
        cls._counter += 1

    @classmethod
    def _dec(cls):
        cls._counter -= 1

    @classmethod
    def get_count(cls):
        return cls._counter

    def __init__(self):
        self._inc()

    def __del__(self):
        self._dec()


class B(A):
    _counter = 0

    def __init__(self, wot):
        super(B, self).__init__()
        self.wot = wot

L=[]
for i in range(3):
  L.append(A())
for i in range(2):
  L.append(B(i))
print "A.count = {}".format(A.get_count())
print "B.count = {}".format(B.get_count())

请注意，我使用了classmethods来确保我们访问了class属性，因为self._counter += 1中的__init__会创建一个实例属性。您也可以使用type(self)._counter += 1（或self.__class__._counter += 1）获得正确的行为，但这有点丑陋imho。

如果这是其他开发人员将在其上构建的API，您可能需要使用自定义元类来确保每个子类都拥有它自己的_counter，即：

 class CounterType(type):
    def __new__(meta, name, bases, attribs):
        if "_counter" not in attribs:
            attribs["_counter"] = 0
        return type.__new__(meta, name, bases, attribs)

class CounterBase(object):
    __metaclass__ = CounterType
    @classmethod
    def _inc(cls):
        cls._counter += 1

    @classmethod
    def _dec(cls):
        cls._counter -= 1

    @classmethod
    def get_count(cls):
        return cls._counter

    def __init__(self):
        self._inc()

    def __del__(self):
        self._dec()


class A(CounterBase):
    pass


class B(A):
    def __init__(self, wot):
        super(B, self).__init__()
        self.wot = wot

L=[]
for i in range(3):
  L.append(A())
for i in range(2):
  L.append(B(i))
print "A.count = {}".format(A.get_count())
print "B.count = {}".format(B.get_count())

Python中完整对象和子对象的计数

1 个答案: