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    <p>Python is a <a href="http://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29" rel="nofollow">garbage collected</a> language. When you do <code>del MyClass</code>, you do not actually delete the 'class object' (classes are objects too), but you only remove the 'name' <code>MyClass</code> from the current namespace, which is some sort of reference to the class object. Any object stays alive as long as it is referenced by something. Since instances reference their own class, the class will stay alive as long as there is at least one instance alive.</p> <p>One thing to be careful about is when you redefine a class (e.g. on the command line):</p> <pre><code>In [1]: class C(object): ...: def hello(self): ...: print 'I am an instance of the old class' In [2]: c = C() In [3]: c.hello() I am an instance of the old class In [4]: class C(object): # define new class and point C to it ...: def hello(self): ...: print 'I am an instance of the new class' In [5]: c.hello() # the old object does not magically become a new one I am an instance of the old class In [6]: c = C() # point c to new object, old class and object are now garbage In [7]: c.hello() I am an instance of the new class </code></pre> <p>Any existing instances of the old class will continue to have the old behavior, which sort of makes sense considering the things I mentioned. The relation between name-spaces and objects is a bit particular to python, but is not that hard once you get it. A good explanation is given <a href="http://effbot.org/zone/python-objects.htm" rel="nofollow">here</a>.</p>
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    1. USBas Swinckels
    1. USBas Swinckels
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    1. COAre the two classes in different namespaces?
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    2. COThere is only one name-space, but two class objects. This is somewhat hard to understand for newcomers or people that have experience with other languages. In my example, I first define the old class, which gets references by the 'name' `C` in the current name-space. When I define the new class, a new class object gets defined and `C` is updated to reference the new class. The old class stays alive, but now without being references by any name. A class object does not know or care about the name that references it. The effbot has a [good explanation](http://effbot.org/zone/python-objects.htm).
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