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POSingleton across modules
 

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    <p>I'm trying to implement a Singleton and I am running into difficulty when I import the module. My set up is the following. I am using Python 2.7.</p> <h3>MODULE 1</h3> <pre><code>class SingletonClass(object): def __new__(self, *args, **kwargs): if not self._instance: self._instance = super(SingletonClass, self).__new__( self, *args, **kwargs) return self._instance print SingletonClass() #OUTPUT: 0x00000000030F1630 print SingletonClass() #OUTPUT: 0x00000000030F1630 (Good, what I want) </code></pre> <h3>MODULE 2</h3> <pre><code>import SingletonClass class AnotherClass: print SingletonClass.SingletonClass() #OUTPUT: 0x0000000003292208 </code></pre> <p>Within the module the singleton is working, but in another module the Singleton is not returning the same object as it did in the first. Any idea why?</p> <h3>Edit</h3> <p>For now I will put the only thing that I have found that works. I'm sure there is a better solution to this, but I think this may better convey what the underlying problem is.</p> <h3>MODULE 1</h3> <pre><code>class SingletonParent(object): _instance = None def __new__(self, *args, **kwargs): if not self._instance: self._instance = super(SingletonParent, self).__new__( self, *args, **kwargs) return self._instance </code></pre> <h3>MODULE 2</h3> <pre><code>import SingletonParent class SingletonClass(object): def __new__(self, *args, **kwargs): if not SingletonParent.SingletonParent._instance: SingletonParent.SingletonParent._instance = super(SingletonClass, self).__new__( self, *args, **kwargs) return SingletonParent.SingletonParent._instance print SingletonClass() #OUTPUT: 0x00000000030F1630 print SingletonClass() #OUTPUT: 0x00000000030F1630 </code></pre> <h3>MODULE 3</h3> <pre><code>import SingletonClass class AnotherClass: print SingletonClass.SingletonClass() #OUTPUT: 0x00000000030F1630 </code></pre> <h1>Solution (Edit 3)</h1> <p>Lesson: Don't have your main function in the same module as your Singleton!</p>
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    1. COpossible duplicate of [Python singleton pattern](http://stackoverflow.com/questions/3037914/python-singleton-pattern)
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    2. COThere's no way that what you have there can possibly work, by which I mean you'll get an error either at the `import` or the `SingletonClass()` in the second module. Also, why's the `print` statement inside a class definition? This code does not make any sense.
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    3. CO@kindall This is pseudo code. It's roughly what I have, but I was trying to simplify things for readability.
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