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POWhy are Python's 'private' methods not actually private?
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copied!<p>Python gives us the ability to create 'private' methods and variables within a class by prepending double underscores to the name, like this: <code>__myPrivateMethod()</code>. How, then, can one explain this</p> <pre><code>>>> class MyClass: ... def myPublicMethod(self): ... print 'public method' ... def __myPrivateMethod(self): ... print 'this is private!!' ... >>> obj = MyClass() >>> obj.myPublicMethod() public method >>> obj.__myPrivateMethod() Traceback (most recent call last): File "", line 1, in AttributeError: MyClass instance has no attribute '__myPrivateMethod' >>> dir(obj) ['_MyClass__myPrivateMethod', '__doc__', '__module__', 'myPublicMethod'] >>> obj._MyClass__myPrivateMethod() this is private!! </code></pre> <p>What's the deal?!</p> <p>I'll explain this a little for those who didn't quite get that.</p> <pre><code>>>> class MyClass: ... def myPublicMethod(self): ... print 'public method' ... def __myPrivateMethod(self): ... print 'this is private!!' ... >>> obj = MyClass() </code></pre> <p>What I did there is create a class with a public method and a private method and instantiate it.</p> <p>Next, I call its public method.</p> <pre><code>>>> obj.myPublicMethod() public method </code></pre> <p>Next, I try and call its private method.</p> <pre><code>>>> obj.__myPrivateMethod() Traceback (most recent call last): File "", line 1, in AttributeError: MyClass instance has no attribute '__myPrivateMethod' </code></pre> <p>Everything looks good here; we're unable to call it. It is, in fact, 'private'. Well, actually it isn't. Running <em>dir()</em> on the object reveals a new magical method that python creates magically for all of your 'private' methods.</p> <pre><code>>>> dir(obj) ['_MyClass__myPrivateMethod', '__doc__', '__module__', 'myPublicMethod'] </code></pre> <p>This new method's name is always an underscore, followed by the class name, followed by the method name.</p> <pre><code>>>> obj._MyClass__myPrivateMethod() this is private!! </code></pre> <p>So much for encapsulation, eh?</p> <p>In any case, I'd always heard Python doesn't support encapsulation, so why even try? What gives?</p>

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