Question

我想在Python3.x中计算自定义类及其子类的实例数。怎么做？非常感谢你。

我尝试过类成员的方式，但它没有用。以下是代码

Base.py

class Base:

    ## class members
    __counter = int(0)
    @classmethod
    def _count(cls):
        cls.__counter += 1
        return cls.__counter

    def __init__(self):
        self.__id = self._count()

    @property
    def id(self):
        return self.__id

SubBase1.py

from Base import Base

class SubBase1(Base):
    def __init__(self):
        Base.__init__(self)

SubBase2.py

from Base import Base

class SubBase2(Base):
    def __init__(self):
        Base.__init__(self)

main.py

from SubBase1 import SubBase1
from SubBase2 import SubBase2

s1 = SubBase1()
s2 = SubBase2()

print('s1-id', s1.id)
print('s2-id', s2.id)

代码输出：

s1-id 1
s2-id 1

但是，我想要的是：

s1-id 1
s2-id 2

我该怎么办？一开始非常感谢你！ PS：环境：Ubuntu 14.04 + Python 3.4 + PyDev

Answer 1

在cls上设置属性将在子类上设置 new 属性。您必须在此处Base明确设置此内容：

class Base:
    __count = 0

    @classmethod
    def _count(cls):
        Base.__count += 1
        return Base.__count

    def __init__(self):
        self.__id = self._count()

    @property
    def id(self):
        return self.__id

如果您尝试在cls上设置属性，则每个类创建唯一的计数器，而不是与所有子类共享。

演示：

>>> class Base: ... __count = 0 ... @classmethod ... def _count(cls): ... Base.__count += 1 ... return Base.__count ... def __init__(self): ... self.__id = self._count() ... @property ... def id(self): ... return self.__id ... >>> class SubBase1(Base): pass ... >>> class SubBase2(Base): pass ... >>> SubBase1().id 1 >>> SubBase1().id 2 >>> SubBase2().id 3 >>> SubBase2().id 4

如何计算自定义类的实例数？

1 个答案: