Floodfill clear solution for Calculate Islands by veky - python coding challenges

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Floodfill solution in Clear category for Calculate Islands by veky
def checkio(data):
    col,result=len(data[0]),[]
    while True:
        size=0
        try: queue={divmod(sum(data,[]).index(1),col)}
        except ValueError: return sorted(result)
        while queue:
            i,j=queue.pop()
            data[i][j]=0
            size+=1
            queue|={(i+di,j+dj) for di in (-1,0,1) if 0<=i+di
                        June 19, 2013

                        
                            Comments:
                            
                                
                                    DoctorProk
 on June 19, 2013, 9:16 a.m.

                                    <pre class='brush: python'>            queue|={(i+di,j+dj) for di in (-1,0,1) if 0&lt;=i+di&lt;len(data)
</pre>

<p>What does this</p>

<pre class='brush: python'>|=
</pre>

<p>do. Can't really make sense out of it.</p>

                                
                            
                                
                                    veky
 on June 19, 2013, 9:45 p.m.

                                    <pre class='brush: python'>            queue|={(i+di,j+dj) for di in (-1,0,1) if 0&lt;=i+di&lt;len(data)
</pre>

<p>I don't see anything in your selection, but I guess you ask about lines 11 and 12. Look up "set comprehensions" in Python 3K.</p>

                                
                            
                                
                                    DoctorProk
 on June 19, 2013, 9:19 a.m.

                                    <pre class='brush: python'>        try: queue={divmod(sum(data,[]).index(1),col)}
</pre>

<p>I looked 'divmod' up in the documentation. Didn't really get, what this built-in is about. Do you mind explaining a little further, what 'divmod' is for?</p>

                                
                            
                                
                                    suwanditan
 on June 19, 2013, 2:45 p.m.

                                    <pre class='brush: python'>        try: queue={divmod(sum(data,[]).index(1),col)}
</pre>

<p>I think this "cryptic" line of code means exactly of this on my code: </p>

<pre class='brush: python'>def getStartingNode( nodes, n ):
    for x, _ in enumerate( list(flatIt(nodes)) ): 
        if _ == 1:
            yield [(x//n), (x%n)]
</pre>

<p>I use this <strong>to extract "the coordinate"</strong>. Well, I learned new trick today then :)</p>

<p>Good job, Veky!</p>

                                
                            
                                
                                    veky
 on June 19, 2013, 9:44 p.m.

                                    <pre class='brush: python'>        try: queue={divmod(sum(data,[]).index(1),col)}
</pre>

<p>I'm always glad when people learn something new about Python reading my code. ;-) Thank you.</p>

                                
                            
                                
                                    veky
 on June 19, 2013, 9:43 p.m.

                                    <pre class='brush: python'>        try: queue={divmod(sum(data,[]).index(1),col)}
</pre>

<p>I won't repeat the documentation. divmod is used here to convert index, which is contiguous 1D coordinate, into 2D coordinates of the first "1" in the data array. Try some examples, I guess it'll be clear.</p>

                                
                            
                                
                                    DoctorProk
 on June 20, 2013, 3:35 p.m.

                                    <pre class='brush: python'>        try: queue={divmod(sum(data,[]).index(1),col)}
</pre>

<p>Oh, I see now. That's just nice. Thanks, veky. Learned a lot today.</p>

                                
                            
                                
                                    DoctorProk
 on June 20, 2013, 12:11 p.m.

                                    <pre class='brush: python'>            queue|={(i+di,j+dj) for di in (-1,0,1) if 0&lt;=i+di&lt;len(data)
</pre>

<p>You guessed right. Don't know why that happened. Yesterday the code was shown correctly. Anyway, thanks for the help. But I still haven't figured out what this "|=" operator is doing to queue with the set as an operand. It's pretty hard to search for it. </p>

                                
                            
                                
                                    veky
 on June 20, 2013, 4:39 p.m.

                                    <pre class='brush: python'>            queue|={(i+di,j+dj) for di in (-1,0,1) if 0&lt;=i+di&lt;len(data)
</pre>

<p>Oh, yes. |= is just a shortcut for set.update . It is logical, since | is union operator for sets, and a|=b does roughly correspond to a=a|b, just as x+=5 roughly corresponds to x=x+5.</p>

<p>Clearer?</p>

                                
                            
                                
                                    bryukh
 on Oct. 31, 2013, 3 a.m.

                                    <p>"Floodfill" is very accurate chosen name.</p>

                                
                            
                                
                                    veky
 on Oct. 31, 2013, 8:51 a.m.

                                    <p>Yes, I enjoy word puns. Thanks. :-)</p>

                                
                            
                                
                                    Ardillo95
 on Oct. 12, 2016, 5:04 a.m.

                                    <p>Wowwwwww I am in love with this solution ^^ I learned a lot!!!
veky, do you think it is a good a idea to base my python learning in only this webpage as a source of knowledge? (and external sources if I have questions)</p>

                                
                            
                                
                                    veky
 on Oct. 13, 2016, 4:25 a.m.

                                    <p>Well, it depends on what you really want to do. If you're a hobby programmer, you'll learn much here, and you don't have to force yourself to read anything else: with time, it will happen naturally.</p>

<p>Even for questions, I'd say this site offers a lot. Just write a question in the comment box (and summon me with `@veky` if you think I should see it) under a solution and someone (most often the solution author) will answer you.</p>

<p>But if you're (trying to become) a professional, keep in mind that this is just a game. It's optimized for fun (and learning in the process), not for solving actual problems with software. Also see <a href="https://py.checkio.org/forum/post/9764/what-was-your-first-job/#comment-43481">this comment</a>.</p>

                                
                            
                                
                                    bsquare
 on Sept. 8, 2019, 6:44 p.m.

                                    <p>Nice solution, like often, thanks!</p>

                                
                            
                                
                                    vlad.bezden
 on Feb. 17, 2020, 6:14 p.m.

                                    <p>as always AWESOME code!!!</p>
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