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copied!<p>I don't think I like this choice of identifiers. It is conventional to start class names with an uppercase letter, so you'd think that you could say <code>isinstance(x, Event)</code>, but you can't. I think a name such as <code>make_event</code> that unambiguously identifies the function as a function would have been better.</p> <p>This issue has already been <a href="http://mail.python.org/pipermail/python-dev/2008-September/082117.html" rel="nofollow">discussed</a> on the mailing list, where the BDFL <a href="http://mail.python.org/pipermail/python-dev/2008-September/082144.html" rel="nofollow">states</a>:</p> <blockquote> <p>This started out as an experiment in API design, where I tried to make things look as much like the similar Java API as possible (I didn't want to invent yet anotherwobbly wheel). I specifically wanted these <em>not</em> to be classes so that people wouldn't start subclassing them. At the time PEP-8 wasn't well established (if at all) and I wanted the factory functions to look like classes. I think in 2.7 / 3.1 we can change the factory functions to conform to PEP-8 (leaving the old names in for a couple of release).</p> </blockquote> <p>The change he mentioned hasn't been done yet, but I think it's pretty safe to say that nowadays the naming scheme is seen as misguided and should not be proliferated.</p> <p>You're right when you say that these factory functions were introduced to mimic a sealed class. The BDFL <a href="http://mail.python.org/pipermail/python-dev/2008-September/082186.html" rel="nofollow">says</a></p> <blockquote> <p>Allowing them to be subclassed makes it harder to replace them on some platforms with equivalent but faster implementations.</p> </blockquote> <p>I don't think this scheme is too common. Most of the time, there is no incentive to replace classes with equivalent implementations, and if a class is not designed for subclassing, you can mention that in the documentation.</p>

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