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POSomething with __new__ and property
 

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    <p>I try to understand the following code from some OpenSource GitHub project. There is a class without <code>__init__</code> but with a <code>__new__</code> method. The code is given as:</p> <pre><code>class Node(object): #pylint: disable=W0404 #Singleton-Pattern _instances = dict() def __new__(cls, name=None): """ Instanciates a node from a file, and (name=None) creates a new node Caution: Filenames are always given relative to the root-dir When no name is given, a new node is created. """ if(name!=None and cls._instances.has_key(name)): return(cls._instances[name]) if(name==None): # a new node, lets find a name for i in itertools.count(0): name = "node%.4d"%i if(cls._instances.has_key(name)): continue# new nodes might not been saved, yet if(path.exists("./nodes/"+name)): continue break self = object.__new__(cls) cls._instances[name] = self #actuall init-code from ZIBMolPy.pool import Pool #avoids circular imports self._pool = Pool() #Pool is a singleton self._name = name self._tmp = Store() #for thing that need to be stored temporarly self._obs = Store() self.parent = None if(path.exists(self.dir)): self.reload() #self.pool.append(self) #register with pool return(self) #--------------------------------------------------------------------------- @property def obs(self): return(self._obs) </code></pre> <p>I found one discussion beween the <code>__init__</code> method and the <code>__new__</code> method at <a href="https://stackoverflow.com/questions/674304/pythons-use-of-new-and-init">Python&#39;s use of __new__ and __init__?</a> According to the highest rated comment, one should only use new if one is subclassing an immutable type like <code>str</code>, <code>int</code>, <code>unicode</code> or <code>tuple</code>. But I think here it is used for some other reason. Further more I don't understand why the class <code>cls</code> should have a name (and why it should have anything todo with some folders) and why I can call </p> <pre><code>n= Node() n.obs </code></pre> <p>like the function obs would be a property function, but it is actually not..</p> <p>I am confused. If your not, I cant wait for your respond.</p>
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