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    <p>The big advantage is that built-in functions (and operators) can apply extra logic when appropriate, beyond simply calling the special methods. For example, <code>min</code> can look at several arguments and apply the appropriate inequality checks, or it can accept a single iterable argument and proceed similarly; <code>abs</code> when called on an object without a special method <code>__abs__</code> could try comparing said object with 0 and using the object change sign method if needed (though it currently doesn't); and so forth.</p> <p>So, for consistency, all operations with wide applicability must always go through built-ins and/or operators, and it's those built-ins responsibility to look up and apply the appropriate special methods (on one or more of the arguments), use alternate logic where applicable, and so forth.</p> <p>An example where this principle wasn't correctly applied (but the inconsistency was fixed in Python 3) is "step an iterator forward": in 2.5 and earlier, you needed to define and call the non-specially-named <code>next</code> method on the iterator. In 2.6 and later you can do it the right way: the iterator object defines <code>__next__</code>, the new <code>next</code> built-in can call it <em>and</em> apply extra logic, for example to supply a default value (in 2.6 you can still do it the bad old way, for backwards compatibility, though in <code>3.*</code> you can't any more).</p> <p>Another example: consider the expression <code>x + y</code>. In a traditional object-oriented language (able to dispatch only on the type of the leftmost argument -- like Python, Ruby, Java, C++, C#, &amp;c) if <code>x</code> is of some built-in type and <code>y</code> is of your own fancy new type, you're sadly out of luck if the language insists on delegating all the logic to the method of <code>type(x)</code> that implements addition (assuming the language allows operator overloading;-).</p> <p>In Python, the <code>+</code> operator (and similarly of course the builtin <code>operator.add</code>, if that's what you prefer) tries x's type's <code>__add__</code>, and if that one doesn't know what to do with <code>y</code>, then tries y's type's <code>__radd__</code>. So you can define your types that know how to add themselves to integers, floats, complex, etc etc, as well as ones that know how to add such built-in numeric types to themselves (i.e., you can code it so that <code>x + y</code> and <code>y + x</code> both work fine, when <code>y</code> is an instance of your fancy new type and <code>x</code> is an instance of some builtin numeric type).</p> <p>"Generic functions" (as in PEAK) are a more elegant approach (allowing any overriding based on a combination of types, <em>never</em> with the crazy monomaniac focus on the leftmost arguments that OOP encourages!-), but (a) they were unfortunately not accepted for Python 3, and (b) they do of course require the generic function to be expressed as free-standing (it would be absolutely crazy to have to consider the function as "belonging" to any single type, where the whole POINT is that can be differently overridden/overloaded based on arbitrary combination of its several arguments' types!-). Anybody who's ever programmed in Common Lisp, Dylan, or PEAK, knows what I'm talking about;-).</p> <p>So, free-standing functions and operators are just THE right, consistent way to go (even though the lack of generic functions, in bare-bones Python, does remove <em>some</em> fraction of the inherent elegance, it's still a reasonable mix of elegance and practicality!-).</p>
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    1. POThe advantages of having static function like len(), max(), and min() over inherited method calls
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    1. USAlex Martelli
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    1. POThe advantages of having static function like len(), max(), and min() over inherited method calls
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    1. CO+1 for a great explanation to the benefits of built-ins.
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    2. COYou say "able to dispatch only on the type of the leftmost argument -- like Python, C++, ..." and then show that python can also dispatch on the right argument with `__radd__`. Also, C++ can dispatch on both arguments if you declare `operator+` as a free function. This seems to be a little inconsistent...
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    3. CO@sth, Python can't _dispatch_ on the RHS argument -- it can _use a builtin or operator_ to do the grunt work. In C++, if `operator+` is a free-standing function, it can be overloaded based on the _statically visible_ (aka compile-time visible) types of the operands, it just **CANNOT** **DISPATCH**, i.e., use strictly the **runtime** types of the operands to pick what code to execute (as a member function can, but based only on the **LEFT HAND SIDE** type). Nothing inconsistent, for readers who knows what dispatch means, and the difference between compile-time and run-time types!-)
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