如何計算自定義類的實例數量？

Question

我想計算Python3.x中自定義類及其子類的實例數。怎麼做？非常感謝你。

我試過類成員的方式，但它不起作用。以下是碼

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) 

的代碼輸出：

s1-id 1 
s2-id 1 

但是，我要的是：

s1-id 1 
s2-id 2 

我該怎麼辦？首先非常感謝！ PS： 環境：Ubuntu的14.04 + Python的3.4 + PyDev的

Answer 1

上cls設置屬性將設置在子類的一個新屬性。你必須明確地設置該上Base這裏：

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 

如果嘗試設置屬性上cls將創建每類獨特的櫃檯，不是所有子類共享。

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