WET creative solution for Moore Neighbourhood by veky - python coding challenges

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WET solution in Creative category for Moore Neighbourhood by veky

count_neighbours=lambda G,r,c:sum(sum(R[c-(c>0):c+2])for R in G[r-(r>0):r+2])-G[r][c]

March 1, 2015

Comments:

veky on March 1, 2015, 4:01 a.m.
Inspired by Zlomovsky's <a href="http://www.checkio.org/mission/count-neighbours/publications/zlomovsky/python-3/lambda-91/#comment-26172">Lambda-91</a> (also known as "WET is shorter than DRY":) solution. They just didn't take it to the extreme. :-D

zlomovsky on March 1, 2015, 12:28 p.m.
Nice :)

vikulin on Oct. 12, 2015, 8:15 p.m.
this time i learned that i can slice beyond upper bounds and walk away with it. man your code is so enlightening!

veky on Oct. 13, 2015, 4:43 a.m.
Slice l[a:b] means 'give me all elements from l, whose indices are in range(a,b)'. I'm sure you see that [2,5,7][1:6] is really the list of all elements from [2,5,7] whose indices i satisfy 1<=i<6. There are only two such elements, 5 and 7. That's different from indexing, where Python has to tell you that no, there is no element at index 5 in that list. But there _is_ a list of such elements, and that list is empty. >>> [element for index, element in enumerate([2,5,7]) if index == 5] [] Monads are interesting. :-)

vikulin on Oct. 13, 2015, 6:42 a.m.
hehe, that's a nice trick to index a single element out of bounds and walk away with it. probably not too efficient though. my obsession is high performance, and your code is not always the speediest one, still almost every time i see your code i learn something new. ty.

veky on Oct. 13, 2015, 9 a.m.
I didn't mean to write that literally, of course that's not efficient. That's just an explanation of the semantics. If you really want to get a slice, just use a slice. <pre class='brush: python'>>>> [2,5,7][5:6] [] </pre> It's ok to be obsessed with performance. It's a bit wrong to be obsessed with performance in Python. Python is really not a great choice for precise reasoning about performance, I have written about that on many occasions. Python is first and foremost, an executable pseudocode. You don't often wonder about performance of pseudocode, right? :-)

vikulin on Oct. 13, 2015, 9:07 a.m.
I was walking with my kids when it suddenly struck me that this whole thing can be shortened to <pre class='brush: python'>>>> l = [2,5,7] >>> i = 5 >>> l[i:i+1] [] </pre> which is more concise and fast.

veky on Oct. 13, 2015, 10 a.m.
While you were walking, I wrote the same thing above. ;-D

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