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copied!<p>I think your intuition is about right.</p> <p>Historically, callable objects (or what I've sometimes heard called "functors") have been used in the OO world to simulate closures. In C++ they're frequently indispensable.</p> <p>However, <code>__call__</code> has quite a bit of competition in the Python world:</p> <ul> <li>A regular named method, whose behavior can sometimes be a lot more easily deduced from the name. Can convert to a bound method, which can be called like a function.</li> <li>A closure, obtained by returning a function that's defined in a nested block.</li> <li>A lambda, which is a limited but quick way of making a closure.</li> <li>Generators and coroutines, whose bodies hold accumulated state much like a functor can.</li> </ul> <p>I'd say the time to use <code>__call__</code> is when you're not better served by one of the options above. Check the following criteria, perhaps:</p> <ul> <li>Your object has state.</li> <li>There is a clear "primary" behavior for your class that's kind of silly to name. E.g. if you find yourself writing <code>run()</code> or <code>doStuff()</code> or <code>go()</code> or the ever-popular and ever-redundant <code>doRun()</code>, you may have a candidate.</li> <li>Your object has state that exceeds what would be expected of a generator function.</li> <li>Your object wraps, emulates, or abstracts the concept of a function.</li> <li>Your object has other auxilliary methods that conceptually belong with your primary behavior.</li> </ul> <p>One example I like is UI command objects. Designed so that their primary task is to execute the comnand, but with extra methods to control their display as a menu item, for example, this seems to me to be the sort of thing you'd still want a callable object for.</p>

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