The below code is a solution I put together for the Project Euler #11 question which asked to find the largest product of 4 numbers of any direction in a matrix (horiz, vertic, and diag all acceptable.)Coding methodology: To me this is the most important. Is the algorithm I used feasible or mostly correct, if not how do I correct it and why won't it work or scale? I realize in some cases there are always going to be optimal solutions that will be over my head mathematically, but generally you can yield a solution that is within a reasonable range of optimal that is passable without knowing a ton of number theory in my experience. Where possible, I hope to learn algorithms along the way (such as the Sieve of Eratosthenes for prime ranges).Coding execution: Given some pseudocode that we determine algorithmically will work, is the code written executed without redundancies and minimizing runtime. As you can see below, my coding is terrible and I'm sure violates many of the principles here. Being more pythonic: Is something I'm not doing pythonic or can it be done simpler with some sort of library I don't know about. I believe this is mostly semantic though in some cases can have large effects on performance (for instance using map() instead of a for loop to apply int()).After looking through another submitted solution on Code Review, I saw that:lines = [s for s in b.splitlines()]bb = []i = 0for line in lines:    bb.append(map(int,lines[i].split()))    i += 1can simplify to:bb = [map(int, row.split()) for row in open('number.txt').read().splitlines()]b = 08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 0849 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 0081 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 6552 70 95 23 04 60 11 42 69 24 68 56 01 32 56 71 37 02 36 9122 31 16 71 51 67 63 89 41 92 36 54 22 40 40 28 66 33 13 8024 47 32 60 99 03 45 02 44 75 33 53 78 36 84 20 35 17 12 5032 98 81 28 64 23 67 10 26 38 40 67 59 54 70 66 18 38 64 7067 26 20 68 02 62 12 20 95 63 94 39 63 08 40 91 66 49 94 2124 55 58 05 66 73 99 26 97 17 78 78 96 83 14 88 34 89 63 7221 36 23 09 75 00 76 44 20 45 35 14 00 61 33 97 34 31 33 9578 17 53 28 22 75 31 67 15 94 03 80 04 62 16 14 09 53 56 9216 39 05 42 96 35 31 47 55 58 88 24 00 17 54 24 36 29 85 5786 56 00 48 35 71 89 07 05 44 44 37 44 60 21 58 51 54 17 5819 80 81 68 05 94 47 69 28 73 92 13 86 52 17 77 04 89 55 4004 52 08 83 97 35 99 16 07 97 57 32 16 26 26 79 33 27 98 6688 36 68 87 57 62 20 72 03 46 33 67 46 55 12 32 63 93 53 6904 42 16 73 38 25 39 11 24 94 72 18 08 46 29 32 40 62 76 3620 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 1620 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 5401 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48lines = [s for s in b.splitlines()]bb = []i = 0for line in lines:    bb.append(map(int,lines[i].split()))    i += 1n = 4count = []row_ct = 0for row in bb:    column_ct = 0    for column in row:        #each case is checking if it's possible to perform the multiplication from left to right        #horizontal         if len(bb) - column_ct >= n:            count.append(bb[row_ct][column_ct]*                          bb[row_ct][column_ct+1]*                          bb[row_ct][column_ct+2]*                          bb[row_ct][column_ct+3])        #vertical        if len(bb) - row_ct >= n:             count.append(bb[row_ct][column_ct]*                          bb[row_ct+1][column_ct]*                          bb[row_ct+2][column_ct]*                          bb[row_ct+3][column_ct])        #downleft        if column_ct >= n and len(bb) - row_ct >= n:            count.append(bb[row_ct][column_ct]*                          bb[row_ct+1][column_ct-1]*                          bb[row_ct+2][column_ct-2]*                          bb[row_ct+3][column_ct-3])        #downright        if column_ct <= len(bb) - n and len(bb) - row_ct >= n:            count.append(bb[row_ct][column_ct]*                          bb[row_ct+1][column_ct+1]*                          bb[row_ct+2][column_ct+2]*                          bb[row_ct+3][column_ct+3])        #column and row_ct are indexes so ie. at third point column_ct will be 3, row count will be        # 0, used for condition checking        column_ct += 1    row_ct += 1max(count)
Multiplying over a matrix
python;beginner;programming challenge;python 2.7;matrix
A few suggestions for improving your code:You can tidy up this line:lines = [s for s in b.splitlines()]to simplylines = b.splitlines()as your list comprehension doesnt affect the elements, and .splitlines() already returns a list in Python 2.7.Indeed, you could go one step further and cut out the lines variable, and iterate over this directly:for line in b.splitlines():Lets break down this loop:bb = []i = 0for line in lines:    bb.append(map(int,lines[i].split()))    i += 1The whole point of using a for foo in bar-style loop is that it saves you doing the index lookups; you can access the variable directly. So you can do away with the i variable, and rewrite it like this:bb = []for line in lines:    bb.append(map(int,line.split()))Generally I think you should prefer list comprehensions to using map(), because it makes for more readable code. Brevity is good; readability is better. Dont squash too much onto one line. So Id expand it slightly like this:bb = []for line in lines:    bb.append([int(num) for num in line.split()])We could reduce this to a one-line list comprehension:bb = [[int(num) for num in line.split()] for line in lines]I think thats right on the cusp of doing too much in a single line. More than two loops within the same list comprehension is definitely too complicated; this is right on the boundary.Personally Id err towards the first construction, but I can also see the case for the second.(Re-reading the question, I see you mention the performance benefits of map() vs a for loop. Unless youre working with very large data sets, the difference is probably negligible. Try not to fall into the trap of premature optimisation.)In this loop:row_ct = 0for row in bb:    column_ct = 0    for column in row:        # do stuff        column_ct += 1    row_ct += 1you should look up the enumerate() function, which can save you from manually managing the indices. It looks like this:for row_idx, row in enumerate(bb):    for col_idx, col in enumerate(row):        # do stuffTry to use more descriptive variable names  bb and n dont tell me much about what these variables represent. Using names that describe your variables will make your code easier to read, review and debug later.Youre storing every possible product, even though youre only interested in the largest. A quick back-of-the-napkin calculation shows that count (another poor variable name, btw) will end up with over 1000 items.Most of them can be thrown away before they're added to count, because they're smaller than an existing product. You should rewrite your program to only store the largest product seen so far  thats a much more scalable approach.