Python的單屬性錯誤

Question

我已經實現了這樣一個單：

class Test123(object):   
    _instance = None 
    def __new__(cls, *args, **kwargs): 
     if not cls._instance: 
      cls._instance = super(Test123, cls).__new__(cls, *args, **kwargs) 
     return cls._instance 

    def initialize(self): 
     self.attr1 = 500 
     self.attr2= 0 
     self.attr3= 0.10 

    def printit(self): 
     print self.attr1 
     print self.attr2 
     print self.attr3 

我不;噸實現__init__，因爲它叫我每次使用Singleton時間，所以要解決它，我只需調用初始化在我的腳本的開始。

每當我運行它：

Test123().initialize() 
time.sleep(1) 
Test123().printit() 

我得到這個錯誤：

Traceback (most recent call last): 
    File "Z:\test\test123.py", line 22, in <module> 
500 
    Test123().printit() 
    File "Z:\test\test123.py", line 17, in printit 
    print self.attr2 
AttributeError: 'Test123' object has no attribute 'attr2' 

任何想法是怎麼回事？我正在使用另一個單身人士，並沒有這樣做。另外，attr1打印得很好，我很困惑。可能它與命名有關，也許其他單例有一個名爲attr2的屬性？

編輯：測試用例看來以後我改回購做工精細，所以這裏是實際的代碼

import MySQLdb 

class DataAccessLayer(): 
    _instance = None 
    def __new__(cls, *args, **kwargs): 
     if not cls._instance: 
      cls._instance = super(DataAccessLayer, cls).__new__(cls, *args, **kwargs) 
     return cls._instance 

    def initialize(self): 
     #init local connection 
     self.dalConnection = 0 
     try: 
      self.dalConnection = MySQLdb.connect('localhost', 'root', 'awesomepassword', 'arb'); 

     except MySQLdb.Error, e: 
      print "Error %d: %s" % (e.args[0],e.args[1]) 

    def __del__(self): 
     self.dalConnection.close() 


    def addrow(self): 
     try: 
      cur = self.dalConnection.cursor() 


      cur.close() 
      self.dalConnection.commit() 

     except MySQLdb.Error, e: 
      print "Error %d: %s" % (e.args[0],e.args[1]) 

DataAccessLayer().initialize() 
DataAccessLayer().addrow() 

創建此錯誤：

Traceback (most recent call last): 
    File "Z:\test\DataAccess.py", line 36, in <module> 
    DataAccessLayer().addrow() 
    File "Z:\test\DataAccess.py", line 25, in addOption 
    cur = self.dalConnection.cursor() 
AttributeError: DataAccessLayer instance has no attribute 'dalConnection' 
Exception AttributeError: "DataAccessLayer instance has no attribute 'dalConnection'" in <bound method DataAccessLayer.__del__ of <__main__.DataAccessLayer instance at 0x00000000022A2748>> ignored 

Answer 1

你DataAccessLayer是一箇舊式類。嘗試class DataAccessLayer(object): ...。

更新：

Class Types

Class types, or 「new-style classes,」 are callable. These objects normally act as factories for new instances of themselves, but variations are possible for class types that override __new__(). The arguments of the call are passed to __new__() and, in the typical case, to __init__() to initialize the new instance.

Classic Classes

Class objects are described below. When a class object is called, a new class instance (also described below) is created and returned. This implies a call to the class’s __init__() method if it has one. Any arguments are passed on to the __init__() method. If there is no __init__() method, the class must be called without arguments.

來源：the python reference

Answer 2

稍微偏離主題，但...這似乎Python的我根本不會。我會嘗試寫一個裝飾類單身，所以我可以做

@Sigleton 
class MySingleton(object): 
    pass 

您也可以重複使用，如果很快，如果你再次需要它的時候......

注：它可以使小的元數據混亂（MySingleton是Singleton的實例，而不是MySingleton），但也許functools.wraps可以幫助某種方式...