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    <p>Is this not documented in the <a href="http://docs.python.org/reference/datamodel.html#special-method-names" rel="nofollow noreferrer">Language Reference</a>? Just from a quick look there, it looks like <code>__cmp__</code> is ignored when <code>__eq__</code>, <code>__lt__</code>, etc are defined. I'm understanding that to include the case where <code>__eq__</code> is defined on a parent class. <code>str.__eq__</code> is already defined so <code>__cmp__</code> on its subclasses will be ignored. <code>object.__eq__</code> etc are not defined so <code>__cmp__</code> on its subclasses will be honored.</p> <p>In response to the clarified question: </p> <blockquote> <p>I know that <code>__eq__</code> is called in preferecne to <code>__cmp__</code>, but I'm not clear why <code>y.__eq__(x)</code> is called in preference to <code>x.__eq__(y)</code>, when the latter is what the docs state will happen.</p> </blockquote> <p>Docs say <code>x.__eq__(y)</code> will be called first, but it has the option to return <code>NotImplemented</code> in which case <code>y.__eq__(x)</code> is called. I'm not sure why you're confident something different is going on here.</p> <p>Which case are you specifically puzzled about? I'm understanding you just to be puzzled about the <code>"b" == tsc</code> and <code>tsc == "b"</code> cases, correct? In either case, <code>str.__eq__(onething, otherthing)</code> is being called. Since you don't override the <code>__eq__</code> method in TestStrCmp, eventually you're just relying on the base string method and it's saying the objects aren't equal.</p> <p>Without knowing the implementation details of <code>str.__eq__</code>, I don't know whether <code>("b").__eq__(tsc)</code> will return <code>NotImplemented</code> and give tsc a chance to handle the equality test. But even if it did, the way you have TestStrCmp defined, you're still going to get a false result.</p> <p>So it's not clear what you're seeing here that's unexpected.</p> <p>Perhaps what's happening is that Python is preferring <code>__eq__</code> to <code>__cmp__</code> if it's defined on <em>either</em> of the objects being compared, whereas you were expecting <code>__cmp__</code> on the leftmost object to have priority over <code>__eq__</code> on the righthand object. Is that it?</p>
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    1. POWhy/When in Python does `x==y` call `y.__eq__(x)`?
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    1. COHaving played with this a bit more, I think you are right that `__eq__` is preferred on either object in these cases.
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