[arethuza]

Sounds like the author of the article has no idea what a multimethod actually is then. :-)

Dynamic binding (in various forms) is arguably a pretty common language feature and generally nothing like as powerful as full multimethod implementations (let alone what is possible in CLOS).

[the_mitsuhiko]

> Sounds like the author of the article has no idea what a multimethod actually is then. :-)

The author (me) knows what multimethods are. I did however not find a better term to refer to the `iter(x)` -> `x.__iter__()` / `x.__getitem__()` concept.

[arethuza]

I'm genuinely interested (not being snarky, honest) - could you explain why you think that expression has anything to do with multimethods? Like I said previously, I'm new to Python and I'm curious what that expression actually means.

[the_mitsuhiko]

> could you explain why you think that expression has anything to do with multimethods?

You can override the behavior of a function based on the types involved. For instance ``coerce(a, b)`` calls ``a.__coerce__(b)``. By overriding ``__coerce__`` for one type you can customize this.

[arethuza]

Do you then have to have conditional code in a.__coerce__(b) to check the type of b and do the appropriate thing?

[zephyrfalcon]

Basically yes. Although there are ways around it: http://www.artima.com/weblogs/viewpost.jsp?thread=101605

[arethuza]

Thanks - that looks quite neat.

It seems to me there is a big difference between having a language that is truly based on multimethods and one where it is possible to implement multimethods fairly easily - from what I can see Python looks more like the latter.

[aidenn0]

That's called "Operator overloading" In this case the operator happens to look like a function, but it's not really any different than a + b -> a.__add__(b)

[DasIch]

That's not just simple operator overloading. What mitsuhiko refers to is that iter() can iterate over an object not just when you implement __iter__() but also when you implement __getitem__() and __len__(), bool() has similar semantics as do several other functions and operators.

[dschoon]

I've always heard them referred to as "Generic Functions", though the Wikipedia article is annoying opaque.

The important quality (in my practical understanding) is that a generic function's specialization is decoupled from the object system -- delegating to `x.__iter__()` doesn't require `x` inheriting a method from a parent; the process `iter(x)` uses to delegate might not even require any type information about `x` at all.