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POHow to dynamically override __setitem__? (no subclass)
 

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  1. POHow to dynamically override __setitem__? (no subclass)
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    <p>I'm not able to override some builtin functions, such as '__setitem__', in <strong>Python2.7</strong> (although the same occurs in previous versions I tested)</p> <p>Although I know this is easy to do via subclassing, this is not what I want here, I need to be able to dynamically override these methods.</p> <p>Apparently, when my class is a subclass of '<strong>object</strong>', the overridden method always ends up calling the original one, but when my class is not an '<strong>object</strong>', it works:</p> <pre><code>&gt;&gt;&gt; def new_implementation(k, v): ... print 'New implementation' ... ### class that extends object &gt;&gt;&gt; class ExtendsObject(object): ... def __setitem__(self, k, v): ... print 'ExtendsObject implementation' ... ### Checking implementation &gt;&gt;&gt; obj = ExtendsObject() &gt;&gt;&gt; obj[0]=0 ExtendsObject implementation ### trying to override setitem, no success &gt;&gt;&gt; obj.__setitem__ = new_implementation &gt;&gt;&gt; obj[0]=0 ExtendsObject implementation ### class that does NOT extends object &gt;&gt;&gt; class DoesNotExtend: ... def __setitem__(self, k, v): ... print 'DoesNotExtend implementation' ... ### Checking implementation &gt;&gt;&gt; obj_2 = DoesNotExtend() &gt;&gt;&gt; obj_2[0]=0 DoesNotExtend implementation ### overriding now works! &gt;&gt;&gt; obj_2.__setitem__ = new_implementation &gt;&gt;&gt; obj_2[0]=0 New implementation </code></pre> <p>For some reason, it seems that objects use some different method resolution order for these built-in functions.</p> <p>Is this a bug? Am I doing something wrong?</p>
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