Wandering Thoughts archives

My current somewhat tangled feelings on operator.attrgetter

In a comment on my recent entry on sort comparison functions, Peter Donis asked a good question:

Is there a reason you're not using operator.attrgetter for the key functions? It's faster than a lambda.

One answer is that until now I hadn't heard of operator.attrgetter. Now that I have it's something I'll probably consider in the future.

But another answer is embedded in the reason Peter Donis gave for using it. Using operator.attrgetter is clearly a speed optimization, but speed isn't always the important thing. Sometimes, even often, the most important thing to optimize is clarity. Right now, for me attrgetter is less clear than the lambda approach because I've just learned about it; switching to it would probably be a premature optimization for speed at the cost of clarity.

In general, well, 'attrgetter' is a clear enough thing that I suspect I'll never be confused about what 'lst.sort(key=operator.attrgetter("field"))' does, even if I forget about it and then reread some code that uses it; it's just pretty obvious from context and the name itself. There's a visceral bit of me that doesn't like it as much as the lambda approach because I don't think it reads as well, though. It's also more black magic than lambda, since lambda is a general language construct and attrgetter is a magic module function.

(And as a petty thing it has less natural white space. I like white space since it makes things more readable.)

On the whole this doesn't leave me inclined to switch to using attrgetter for anything except performance sensitive code (which these sort()s aren't so far). Maybe this is the wrong decision, and if the Python community as a whole adopts attrgetter as the standard and usual way to do .sort() key access it certainly will become a wrong decision. At that point I hope I'll notice and switch myself.

(This is an sense an uncomfortable legacy of CPython's historical performance issues with Python code. Attrgetter is clearly a performance hack in general; if lambda was just as fast as it I'd argue that you should clearly use lambda because it's a general language feature instead of a narrowly specialized one.)