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    <blockquote> <p>When and how are static methods suppose to be used in python?</p> </blockquote> <p>The glib answer is: Not very often.</p> <p>The even glibber but not quite as useless answer is: When they make your code more readable.</p> <hr> <p>First, let's take a detour to <a href="http://docs.python.org/2/library/functions.html#staticmethod" rel="noreferrer">the docs</a>:</p> <blockquote> <p>Static methods in Python are similar to those found in Java or C++. Also see <code>classmethod()</code> for a variant that is useful for creating alternate class constructors.</p> </blockquote> <p>So, when you need a static method in C++, you need a static method in Python, right?</p> <p>Well, no.</p> <p>In Java, there are no functions, just methods, so you end up creating pseudo-classes that are just bundles of static methods. The way to do the same thing in Python is to just use free functions. </p> <p>That's pretty obvious. However, it's good Java style to look as hard as possible for an appropriate class to wedge a function into, so you can avoid writing those pseudo-classes, while doing the same thing is bad Python style—again, use free functions—and this is much less obvious.</p> <p>C++ doesn't have the same limitation as Java, but many C++ styles are pretty similar anyway. (On the other hand, if you're a "Modern C++" programmer who's internalized the "free functions are part of a class's interface" idiom, your instincts for "where are static methods useful" are probably pretty decent for Python.)</p> <hr> <p>But if you're coming at this from first principles, rather than from another language, there's a simpler way to look at things:</p> <p>A <code>@staticmethod</code> is basically just a global function. If you have a function <code>foo_module.bar()</code> that would be more readable for some reason if it were spelled as <code>foo_module.BazClass.bar()</code>, make it a <code>@staticmethod</code>. If not, don't. That's really all there is to it. The only problem is building up your instincts for what's more readable to an idiomatic Python programmer.</p> <p>And of course use a <code>@classmethod</code> when you need access to the class, but not the instance—alternate constructors are the paradigm case for that, as the docs imply. Although you often <em>can</em> simulate a <code>@classmethod</code> with a <code>@staticmethod</code> just by explicitly referencing the class (especially when you don't have much subclassing), you shouldn't.</p> <hr> <p>Finally, getting to your specific question:</p> <p>If the only reason clients ever need to look up data by ID is to construct an <code>Entity</code>, that sounds like an implementation detail you shouldn't be exposing, and it also makes client code more complex. Just use a constructor. If you don't want to modify your <code>__init__</code> (and you're right that there are good reasons you might not want to), use a <code>@classmethod</code> as an alternate constructor: <code>Entity.from_id(id_number, db_connection)</code>.</p> <p>On the other hand, if that lookup is something that's inherently useful to clients in other cases that have nothing to do with <code>Entity</code> construction, it seems like this has nothing to do with the <code>Entity</code> class (or at least no more than anything else in the same module). So, just make it a free function.</p>
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