Say what you want clear solution for Easy Unpack by veky - python coding challenges

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Say what you want solution in Clear category for Easy Unpack by veky

from operator import itemgetter
easy_unpack = itemgetter(0, 2, ~1)

Oct. 11, 2017

Comments:

oduvan on Oct. 11, 2017, 11:26 a.m.
sweet!!

veky on Oct. 11, 2017, 1:20 p.m.
Semantic sugar. :-D

ElliotG on May 26, 2018, 6:23 p.m.
Very concise and clever to use itemgetter! Using a bitwise 'not' of 1 to represent -2 is a little too clever, and obfuscates the program intent. More details for those less familiar with binary representation, using 8 bits: 1 = b00000001; -2 = b11111110; ~1 = b11111110; or more simply ~1 == -2 However, as a learning exercise it was effective in having me lookup the bitwise not operator ;) Well Done!

veky on May 28, 2018, 11:44 a.m.
You're subtly wrong about the intent, and factually wrong about the implementation. Please read <a href="https://py.checkio.org/mission/median/publications/veky/python-3/both-sides/share/63e9bd8840f814430eb543a064990714/#comment-23114">this comment</a> (and other comments on that solution if you have time), and if you still have questions, feel free to ask.

ElliotG on May 28, 2018, 4:54 p.m.
Thanks for your reply and for sharing your other post. After having read the post, I understand your intent. The use in the median problem seems more useful, than in this example where a literal is used. This is a very interesting idiom. I do not understand your comment about being factually wrong about the implementation. The '~' operator is a bitwise not, correct? The rest is 2's complement representation of a signed int. Right?

veky on May 29, 2018, 6:43 a.m.
First paragraph: well, if you start to think about "indexing from the other side" as "indexing flipped", it will become more natural to think that way even in this case. Look at the text: <pre class='brush: python'>first, third and second to the last </pre> If first is `[0]` (offset zero), third is `[2]` (offset two), isn't it very natural that second to the last be `[~1]` (offset one flipped)? <hr /> Second paragraph: ah, so you didn't read the whole thread. :-) Ok, read <a href="https://py.checkio.org/mission/median/publications/veky/python-3/both-sides/share/63e9bd8840f814430eb543a064990714/#comment-36966">this comment</a> too. TLDR: there is no "using n bits", because there is no "n". Python ints are not stuffed into boxes of finite size.

ElliotG on May 29, 2018, 12:47 p.m.
Thanks again. A very useful idiom. There is no debate on the underlying implementation, you said it well "what’s important is x|~x==~0 (universal set of bits) and x&~x==0 (empty set of bits), in other words, ~ is exactly the set complement operation."

veky on May 29, 2018, 2:38 p.m.
I don't know, you said something about 8 bits above. :-) The point is, "universal set of bits" is infinite.

hugoboss on Aug. 10, 2018, 1:34 p.m.
my jaw is down... What the hell is ~? I'm gone. Another pile of documentation waits for me:)

veky on Aug. 11, 2018, 3:31 a.m.
Documentation is boring. My comments are much better. Read them above. :-D

hugoboss on Aug. 11, 2018, 8:59 a.m.
OK

Str3et on Dec. 17, 2018, 7:21 a.m.
nice! Thanks.

veky on Dec. 17, 2018, 5:04 p.m.
You're welcome. :-)

matdibobe on Feb. 3, 2019, 11:14 p.m.
So what does the code return(), because I tried the exact code above but I get an assertion error.

veky on Feb. 5, 2019, 8:30 a.m.
The code doesn't return() anything (and return is not a function, so I don't know what the parentheses are doing there). It names a particular itemgetter by the name easy_unpack. Where did you try the code, and what error message did you get?

lifeshow30s on July 9, 2020, 8:32 a.m.
You better think itemgetter work like this. itemgetter()() Assertions provide tuples as index.

veky on July 9, 2020, 3:27 p.m.
I'm not sure what assertions are doing there, but yes, itemgetter returns a function. <pre class='brush: python'>itemgetter(i, j)(x) ~~~> (x[i], x[j]) </pre>

kravagyan on April 5, 2019, 5:50 a.m.
just wow!

z.thami on May 15, 2019, 11:38 a.m.
Nice!

shadetoraven on June 29, 2019, 1:20 p.m.
nice

DragonMachinations on Aug. 5, 2019, 9:16 p.m.
Fine, take my +. I normally think it's obnoxious when you guys import stuff from operator in these simple tasks, but this is so elegant that I am obligated to respect it. Nicely done.

veky on Aug. 5, 2019, 9:23 p.m.
Language is language, with all its features. In most cases there is still one obvious way to do it. Sometimes that one obvious way lies in the operator module. Why not use it then? The simplicity of the task has nothing to do with that. You probably think it's obnoxious since you've seen examples when people overcomplicate things by importing a chisel and then using it to drive screws. But there is a right way to use operator (and chisel, of course;).

not_real on Aug. 8, 2019, 5:08 p.m.
Maybe `easy_unpack = itemgetter(0, 2, -2)` is more "clear"? (But not as entertaining as using `~1`)

veky on Aug. 8, 2019, 5:13 p.m.
It's not (only) about entertainment. Python counts from 0. Counting one side form 0 and another one from 1 is ugly and invites off-by-one errors. Even you'd probably admit that you thought twice about that 2 and -2. It simply looks wrong.

not_real on Aug. 8, 2019, 5:29 p.m.
Negative index is a "landmine" on it's own, but `~` similarity to `-` is a stealthier one. Until I read the comments my attention only got caught by `itemgetter` overlooking that `-1` couldn't work.

veky on Aug. 8, 2019, 6:07 p.m.
So, I'm giving you a way to avoid the landmine, just at the price of a crisper font. Not a bad deal IMO. 😃

sanello on Aug. 22, 2019, 7:02 p.m.
Very nice!

bsquare on Sept. 18, 2019, 2:02 p.m.
Haha, great!

Anton_Tushinskij on Dec. 23, 2019, 5:39 a.m.
How to output a tuple in result?

muneerkhan31886 on Feb. 6, 2020, 9:48 a.m.
Thanks Buddy! what i have learn new today was this ~ bitwise operator your work is appreicated!!!

Dascal on Feb. 12, 2020, 4:42 p.m.
Correct me if I am wrong. A negative index is implemented as the length of the array plus a negative index value (length(a) + [-i]). In pseudo code 1. Take the length of the array 2. Add the index value of [-2] to the length of the array In your case, it will be: 1. Take the length of the array 2. Do a bit operation 3. Add the result of point 2 to the length of the array So each call of your function will perform an additional bit operation.

veky on Feb. 12, 2020, 5:02 p.m.
It depends on whether you include the peephole optimizer into consideration---but in both cases you're wrong. It's totally symmetrical. `-` is an unary operator in much the same way as `~` is. Look: <pre class='brush: python'>>>> dis.dis('[][-a]') 1 0 BUILD_LIST 0 2 LOAD_NAME 0 (a) 4 UNARY_NEGATIVE 6 BINARY_SUBSCR 8 RETURN_VALUE >>> dis.dis('[][~a]') 1 0 BUILD_LIST 0 2 LOAD_NAME 0 (a) 4 UNARY_INVERT 6 BINARY_SUBSCR 8 RETURN_VALUE </pre> Of course, if instead of `a` you use `2`, then `-2` will be precalculated and stored in the bytecode as constant---but so will `~1`. If anything, you might argue that bit invert is simpler for the processor to execute, than unary minus (which is <a href="https://www.cs.cornell.edu/~tomf/notes/cps104/twoscomp.html">bit invert, followed by adding one</a>:). But of course, since there is a long way from the Python int to the processor register, it doesn't matter in the slightest. :-)

Adolf_Igorev on April 5, 2020, 7:38 a.m.
Really elegant

xg3572 on May 29, 2020, 12:29 a.m.
You smells like cool guy

veky on May 29, 2020, 2:40 a.m.
As long as you still have the sense of smell, you're probably COVID-free. ;-D

nguyenlk93 on Nov. 1, 2020, 2:13 p.m.
wo

veky on Nov. 1, 2020, 2:15 p.m.
ow?

samhuawey on Dec. 4, 2020, 8:34 a.m.
Long and ineffective

veky on Dec. 4, 2020, 9:07 a.m.
On the contrary, I'd say it's very effective. Now do you have any arguments for your claim? About "long", it's one call from the standard library. I'm not quite sure how it could be shorter in a meaningful sense. :-)

kdim on Jan. 26, 2021, 8:38 p.m.
It's a very cool! You are Rock!

veky on Jan. 26, 2021, 9:01 p.m.
... Gazing from my window to the streets below On a freshly fallen silent shroud of snow (<a href="https://www.youtube.com/watch?v=JKlSVNxLB-A)">https://www.youtube.com/watch?v=JKlSVNxLB-A)</a> :-D

Verstov on Jan. 9, 2022, 10:57 a.m.
Now I know about '~'. Thanks! =)

Reddik on Nov. 10, 2022, 11:12 a.m.
Ого!

veky on Nov. 10, 2022, 3:38 p.m.
Hm? :-)

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