2016-01-20 | 846 words | Attempting to answer most commonly asked Python StackOverflow questions in Perl 6.
As a Perl 5 programmer of about a decade, I'm well aware of how it was referred to at some point or another as the "write-only" and "linenoise" language. With the newest addition of the baby Perl 6 language to the Perl family, I fear that I must
declare (wildly speculate) based on my extensive research (a boring ride on a bus, while staring at my phone) that Python steals that title now!!
Why Python? Blame whoever made the Stackoverflow Python Report scroll through my Twitter feed. I merely picked two problems from that list and asked myself what would the Perl 6 solutions to them look like.
Interleave Two Strings
The top rated item of the week is interleaving two strings.
#Given: u = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' l = 'abcdefghijklmnopqrstuvwxyz' #Wanted: 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz'
The accepted Python answer is this:
res = "".join(i + j for i, j in zip(u, l)) print(res)
Certainly isn't bad, but using a two-variable postfix
for loop inside a method call is something I wouldn't want to read in code very often. Let's examine the Perl 6 version:
say join '', (u.comb Z l.comb)
Just like the Python version, we're utilizing the
join(), but the rest looks certainly cleaner: we're using the
.comb method on our two strings, which without arguments returns characters in a string, and we combine them with the
Z zip operator. That is it! No loops needed. (And before someone points it out, no, I haven't missed any sigils. Perl 6 can have sigilless vars, baby).
Round-Robin Merge Two Lists of Different Length
Another interesting item on the list is round-robin merge of two different-length lists. There isn't an accepted answer to the question, so I'll go with the highest-voted:
list1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] list2 = ['x', 'y'] n = 3 iter1 = iter(list1) res =  for x in list2: res.extend([next(iter1) for _ in range(n - 1)]) res.append(x) res.extend(iter1) >>> res ['a', 'b', 'x', 'c', 'd', 'y', 'e', 'f', 'g', 'h']
I see a
for loop, and another
.extend method and then
.append method and after another
.extend after the outer
for loop, voilà! Result.
Being a Perl 6 noob, I first reached for the trusty
Z operator, then I messed with the Hyper Operators, and all I got in return were either wrong solutions or messy solutions... Until someone pointed out that Perl 6 actually has a
roundrobin routine! So what's the Perl 6 answer?
my @list1 = 'a' .. 'h'; my @list2 = <x y>; say flat roundrobin @list1, @list2; # >>> # OUTPUT«a x b y c d e f g h»
On the first two lines, we're simply creating two variables for our lists.
@list1 uses a range with letters and
@list2 uses the quote word construct. I'm sure similar things exist in Python too, so I won't count clarity and ease-of-writing points for those, but the rest of the code is rather different. There are no loops, extends, or appends. We use the
roundrobin routine to... surprise... round-robin through the two lists. Now, it returns a
Lists, which is why I added the
flat routine as well, to flatten the output to what the Python answer returns.
EDIT: as one of the commenters pointed out, I wasn't paying much attention to this one and completely missed the "nth element" requirement. Never fear, however, the alternate requirement only needs the addition of trusty
.rotor List method that breaks up a list into sublists:
my @list1 = 'a' .. 'h'; my @list2 = <x y>; my $n = 3; say flat roundrobin @list1.rotor($n - 1, :partial), @list2; # >>> # OUTPUT«a b x c d y e f g h»
This post is, of course, a tongue-in-cheek joshing, based on a random post I saw on Twitter. However, on a more serious and deeper note, it does seem that the brand-new language like Perl 6 that has an actual language specification, when compared to an old grandpa specless language like Python, seems to offer built-in methods, operators, and subroutines specifically geared to real-world problems that—for however short a period of time—made it to the top of a popular programming question website.
And now, if you'll excuse me, I'm off to make a silly YouTube video declaring Python to be the new "Write-only, Linenoise" language. Sorry, Perl. You lose.
As I'm not the one to shyly sit in a silo, I went to #python on irc.freenode.net and asked for feedback on this article, and it's this:
In the first example, the use of the for loop is extremely idiomatic Python, so the code is perfectly readable to a competent Python programmer. As for the second Python example, the general opinion was that it's overly-complex and I did see a simple 1-line round-robin example presented to me in-channel. The nth element variant may be dropped to me on Twitter as well in the future :)
I stayed for some drinks, there was cake too! And then I left the channel...