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> 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 fi

> 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 15y ago
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 15y ago
  > 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 15y ago
    Do you then have to have conditional code in a.__coerce__(b) to check the type of b and do the appropriate thing?
    - zephyrfalcon 15y ago
      Basically yes. Although there are ways around it: http://www.artima.com/weblogs/viewpost.jsp?thread=101605 http://www.artima.com/weblogs/viewpost.jsp?thread=101605
      - arethuza 15y ago
        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 15y ago
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 15y ago
  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 15y ago
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.

arethuza 15y ago

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 15y ago
> 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 15y ago
  Do you then have to have conditional code in a.__coerce__(b) to check the type of b and do the appropriate thing?
  - zephyrfalcon 15y ago
    Basically yes. Although there are ways around it: http://www.artima.com/weblogs/viewpost.jsp?thread=101605 http://www.artima.com/weblogs/viewpost.jsp?thread=101605
    - arethuza 15y ago
      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 15y ago

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 15y ago
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 15y ago

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.