Python 中完整对象和子对象的计数

Question

我想维护 A 和 B 对象的计数，B 是 A 的子类。因此计数应该特定于 A 和 B。例如，如果我创建 3 个 A 对象和 2 个 B 对象，凭借在构造函数调用中，A 的计数变为 3+2=5，但我想保留为 3（当用作 B 的子对象时不是）。请评论以下代码片段：

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)

输出为：

A.acount = 3
B.bcount = 2

Answer 1

你让它变得复杂 - 你所需要的只是为每个 class:

有一个独特的 count class 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 classmethods 来确保我们正在访问 class 属性，因为 __init__ 中的 self._counter += 1 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，但这有点难看。

如果这是 API 其他开发者将以此为基础的，您可能需要使用自定义元 class 来确保每个子 class 都有自己的 _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

Count of full objects and subobjects in Python

python

class

class-variables

subobject