[Python-Dev] any support for a methodcaller HOF? (original) (raw)

Michael Hudson mwh at python.net
Fri Feb 3 10:36:30 CET 2006

Alex Martelli <aleaxit at gmail.com> writes:

I was recently reviewing a lot of the Python 2.4 code I have written, and I've noticed one thing: thanks to the attrgetter and itemgetter functions in module operator, I've been using (or been tempted to use) far fewer lambdas, particularly but not exclusively in key= arguments to sort and sorted.

Interesting. Something I'd noticed was that until the key= argument to sort appeared, I was hardly using any lambdas at all (most of the places I had used them were rendered obsolete by list comprehensions).

Most of those "lambda temptations" will be removed by PEP 309 (functional.partial), and most remaining ones are of the form: lambda x: x.amethod(zip, zop)

So I was thinking -- wouldn't it be nice to have (possibly in module functional, like partial; possibly in module operator, like itemgetter and attrgetter -- I'm partial to functional;-) a methodcaller entry akin to (...possibly with a better name...): def methodcaller(methodname, *a, **k): def caller(self): getattr(self, methodname)(*a, **k) caller.name = methodname return caller ...? This would allow removal of even more lambdas. I'll be glad to write a PEP, but I first want to check whether the Python-Dev crowd would just blast it out of the waters, in which case I may save writing it...

Hmm.

funcTakingCallback(lamda x:x.method(zip, zop)) funcTakingCallback(methodcaller("method", zip, zop))

I'm not sure which of these is clearer really. Are lambdas so bad? (FWIW, I haven't internalized itemgetter/attrgetter yet and still tend to use lambdas instead those too).

A class I wrote (and lost) ages ago was a "placeholder" class, so if 'X' was an instance of this class, "X + 1" was roughly equivalent to "lambda x:x+1" and "X.method(zip, zop)" was roughly equivalent to your "methodcaller("method", zip, zop)". I threw it away when listcomps got implemented. Not sure why I mention it now, something about your post made me think of it...

Cheers, mwh

-- If you give someone Fortran, he has Fortran. If you give someone Lisp, he has any language he pleases. -- Guy L. Steele Jr, quoted by David Rush in comp.lang.scheme.scsh

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