smn theorem creative solution for Absolute Sorting by veky - python coding challenges

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smn theorem solution in Creative category for Absolute Sorting by veky

from functools import partial as c
checkio=c(sorted,key=abs)

July 1, 2014

Comments:

mscmorris on Feb. 6, 2015, 10:30 p.m.
Great! Nice to know Python has a library for partial application already available.

veky on Feb. 6, 2015, 10:45 p.m.
Python has <a href="http://xkcd.com/353/">everything</a> already available. You just have to dare to wish. :-D

bryanandrade on July 27, 2015, 1:11 p.m.
Thanks for sending me the link to this solution. 3 thumbs up!

veky on July 29, 2015, 7:06 a.m.
Thank you. :-)

tarjeii on Nov. 1, 2015, 9:19 p.m.
Thanks for teaching us something "new", 3 thumbs up

veky on Nov. 2, 2015, 5:12 a.m.
That's my main meta-mission here. :-)

oglop on Dec. 17, 2015, 1:36 p.m.
Could you please explain me the difference between: <pre class='brush: python'>checkio = lambda nums: sorted(nums, key=abs) </pre> and what partial is good for? I read the documentation but it didn't help me. Thanks

veky on Dec. 20, 2015, 3:15 p.m.
The difference is the same as the difference between filter/map and generator expressions, which I've <a href="http://www.checkio.org/mission/clock-angle/publications/veky/python-3/there-and-back-again/#comment-20963">written about</a> here before. Read that post for many details. In short, `partial` is an ordinary higher-order function, and as such is directly Pythonic - Python gives you access to objects, with a very tame grammar and standard evaluation order. Some of these objects might be functions, but they are accessed in exactly the same way as any other argument: their identity is ascertained in the moment of higher-order call, and their attributes (including `call` attribute in case of functions:) are accessed when needed, usually later in the moment of lower-order call. On the other hand, `lambda` is a quote - LISP people would probably call it a macro. It is a special syntactic form: you can't write a function that acts the same as `lambda` keyword, because its "arguments" would be evaluated at the moment of syntactical construction. Python usually does not give you normal access to code itself, prefering you to distinguish code and data. In code there are no objects, just names for them - which are resolved in a complex hierarchy of namespaces according to rules which are not exactly simple. As just one example where lambda as code, accessing names just as any function, directly clashes with many people's intuitions, see <a href="https://www.checkio.org/forum/post/1353/lambda-comprehension-challenge/">this post</a> (and <a href="https://www.checkio.org/forum/post/1353/lambda-comprehension-challenge/#comment-8578">my answer</a>). There, one would like to say that i is just a parameter to the lambda construction, but it isn't. Both lambdas there are completely the same (because they have the same code), and both of them return i when called. On the other hand, if the puzzle used `partial`s, <pre class='brush: python'>[partial(identity, i) for i in 'ab'][0]() </pre> then it wouldn't be a puzzle at all, would it? :-) It's perfectly natural to reason about partials, since they are first-class objects. lambdas on the other hand are a syntactical construct, like a genexp or a loop. It's sad that people use lambda when a partial (or a builtin, or a function from operator module, or a special method...) would be much more suitable. * You can define <pre class='brush: python'>def identity(x): return x or even identity = lambda x: x </pre> but note that this usage of lambda is not problematic, since x is a parameter to identity, and a different value is substituted for it in each element above. Of course, that means you can have best of both worlds with <pre class='brush: python'>[lambda *, _i=i: _i for i in 'ab'][0]() </pre> but that again is probably too complicated. :-)

DahliaSR on Oct. 13, 2016, 7:58 p.m.
Learned something new - again! If I got it wright, using functools.partial() makes most sense if you are actually planning to reuse the partial object?

veky on Oct. 14, 2016, 6:55 a.m.
Yes, but that's so for naming in general. You usually name some partial (pun accidental) result if you intend to reuse it. Otherwise you'd just inline it. If I wanted to sort a concrete list l by abs, I'd just write <pre class='brush: python'>l.sort(key=abs) </pre> and be done with it. But not necessarily. In some cases it still pays to have a once-used partial named, since name can serve as a documentation. <pre class='brush: python'>fromhex = functools.partial(int, base=16) </pre>

DahliaSR on Oct. 14, 2016, 6:59 p.m.
That is a GOOD point. <blockquote> But not necessarily. In some cases it still pays to have a once-used partial named, since name can serve as a documentation. </blockquote>

titaevskaya on Sept. 7, 2021, 4:29 p.m.
Great really simple and in python style. I'll also try to use functools library after this task. Thank you!

Alex_4444D on Oct. 20, 2021, 9:53 p.m.
waw nice :)

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