Python单例属性错误

Python singleton attribute error

我有一个这样的单例实现：

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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

我不实现uu init_uuu，因为每次使用singleton时都会调用它，所以为了绕过它，我只在脚本开始时调用initialize。

每当我运行它时：

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

我得到这个错误：

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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'

你知道怎么回事吗？我用的是另一个单件，它不这样做。另外，ATTR1打印得很好，我很困惑。它可能与命名有关，也许其他的单例有一个名为attr2的属性？

编辑：在我更改了repo之后，测试用例似乎工作正常，所以这里是实际的代码

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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()

创建此错误：

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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

相关讨论

你的DataAccessLayer是一个老式的班级。试试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.

源：python引用