If by no brainer you mean the performance of __sort-key__ is always better of __lt__

No. By no-brainer I meant that IF there is a __sort_key__ defined, then it should be used for sorting, regardless of whether __lt__ is also defined. (min and max should probably prefer __lt__)

I will wask for a proof in the form of benchmarks with enough use-case coverage.

Indeed — I was surprised that it helped so much, and didn’t seem to hurt for the one example.

But the greater concern is that this will effect every sort (that doesn’t provide a key function) so if there is any noticeable performance hit, that probably kills the idea.

And the most risky example is lists of ints or floats — which are very fast to compare. So adding a method lookup could be a big impact.

I’m not sure how to benchmark that without hacking the sorting C code though.

I’d still love to know if my benchmark attempt was at all correct for custom classes in any case.

def outer_key(item):
return item.key()

so we get a function lookup each time it's used.

However, I'm confused by the results -- essentially NO Change. That extra method lookup is coming essentially for free. And this example is using a tuple as the key, so not the very cheapest possible to sort key.

Did I make a mistake? is that lookup somehow cached?

In [36]: run sort_key_test.py
10000
key 0.012529s 10000 calls
outer_key 0.012139s 10000 calls
lt 0.048057s 119877 calls

each run gives different results, but the lt method is always on order of 5X slower for this size list. Sometimes out_key is faster, mostly a bit slower, than key.

Also, I tried making a "simpler" __lt__ method:

return (self.value1, self.value2) < (other.value1, other.value2)

but it was bit slower than the previous one -- interesting.

This is more expensive to execute then my version for 2 reasons.

1) my __lt__ did not need to create any tuples.

2) my __lt__ can exit after only looking at the value1's

Then I tried a simpler (but probably common) simple attribute sort:

def __lt__(self, other):
global lt_calls
lt_calls += 1

return self.value1 < other.value1

def key(self):
global key_calls
key_calls += 1

return self.value1

And that results in about a 6X speedup

In [42]: run sort_key_test.py
10000
key 0.005157s 10000 calls
outer_key 0.007000s 10000 calls
lt 0.041454s 119877 calls
time ratio: 5.922036784741144

And, interestingly (t me!) there is even a performance gain for only a 10 item list! (1.5X or so, but still)

My guess is that this is because the __lt__ test on simple types is very fast in python.

_______________________________________________
Python-ideas mailing list
Python-ideas@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/