Five-minute Multimethods in Python

Re:Five-minute Multimethods in Python by icebraining on Wednesday December 07, 2011 @09:36AM (#3323907)

Because a switch can usually be replaced by a dictionary?

    { 1: runOne, 2: runTwo, 3:runThree }[n]()

is equivalent to

    switch(n) { 
        case 1: runOne(); break; 
        case 2: runTwo(); break;
        case 3: runThree(); break;
    }

[ Parent | on HN ]

Re:Five-minute Multimethods in Python by adobriyan on Wednesday December 07, 2011 @09:46AM (#3323945)

This forces programmer to invent dummy names. And Python doesn't support nontrivial lambdas.

[ Parent | on HN ]

Re:Five-minute Multimethods in Python by mhb on Wednesday December 07, 2011 @09:47AM (#3323946)

I've seen the argument about why that's more "pythonic", but it's not compelling. Allowing some syntactic sugar would make the meaning a lot more obvious.

[ Parent | on HN ]

Re:Five-minute Multimethods in Python by DanielRibeiro on Wednesday December 07, 2011 @09:46AM (#3323944)

Also, on Smalltalk (which influenced python) there is no switch statement as well. On the other hand, Smalltalk has no if, while, for statements as well (they are all methods).

[ Parent | on HN ]

Re:Five-minute Multimethods in Python by gecko on Wednesday December 07, 2011 @10:47AM (#3324244)

While Smalltalk doesn't have case statements, a) it's trivial to add them, and b) the way you get around it is totally different: rather than use a Dictionary, you instead generally make a pile of tiny classes, each with a fooBar: method, and then simply make sure you've got the right object type and call fooBar: on it indiscriminately--in other words, basically your classic visitor pattern.

That's totally possible in Python, too, but I don't really ever see it done.

[ Parent | on HN ]

Re:Five-minute Multimethods in Python by datashaman on Wednesday December 07, 2011 @11:16AM (#3324388)

I like to use defaultdict for this. A strategy dictionary, with a default strategy.

dispatch = defaultdict(default_stategy)

dispatch['one'] = new_strategy

print dispatch['two'] => default_strategy.

Beats case statements and elif chains.

[ Parent | on HN ]

Re:Five-minute Multimethods in Python by zeekay on Wednesday December 07, 2011 @12:36PM (#3324807)

I usually just provide a default argument to get:

dispatch.get('two', default_strategy)

[ Parent | on HN ]

Re:Five-minute Multimethods in Python by jronkone on Wednesday December 07, 2011 @03:21PM (#3325766)

Consing for control-flow is not normal, but on Python it is. Python - not even once.

[ Parent | on HN ]