On 24/03/2011 23:49, Steven D'Aprano wrote:
On Thu, 24 Mar 2011 17:47:05 +0100, Antoon Pardon wrote:
However since that seems to be a problem for you I will be more
detailed. The original poster didn't ask for cases in which cmp was
necessary, he asked for cases in which not using cmp was cumbersome.
I'm the original poster, and that's not what I said. I said:
"If anyone has any use-cases for sorting with a comparison function that
either can't be written using a key function, or that perform really
badly when done so, this would be a good time to speak up."
You'll notice that I said nothing about whether writing the code was easy
or cumbersome, and nothing about readability.
I
gave a case where not using cmp was cumbersome. a tuple where you want
it sorted with first item in descending order and second item ascending.
No, I'm sorry, calling sort twice is not cumbersome. In fact, if somebody
gave me code that sorted tuples in that way using a comparison function,
I would immediately rip it out and replace it with two calls to sort: not
only is it usually faster and more efficient, but it's easier to read,
easier to reason about, and easier to write.
from operator import itemgetter
data.sort(key=itemgetter(1))
data.sort(key=itemgetter(0), reverse=True)
If there are two, it isn't too bad, but if there are several (some
ascending, some descending), then it gets a little cumbersome.
A cmp function for this task may have been justified back in the Dark
Ages of Python 2.2, before Python's sort was guaranteed to be stable, but
there's no need for it now.
[snip]
It's one of those things I wouldn't have voted to remove, but now it's
gone, I'm unsure how much I'd like it back! I wouldn't object to it
returning...
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