How on Earth does ^.?$|^(..+?)\1+$ produce primes?

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  • Опубліковано 22 гру 2024
  • Take your personal data back with Incogni! Use code standupmaths at the link below and get 60% off an annual plan: incogni.com/st...
    ^.?$|^(..+?)\1+$
    Props will be for sale here: www.ebay.co.uk...
    Fantastic blog post by Illya Gerasymchuk. "Demystifying The Regular Expression That Checks If A Number Is Prime" illya.sh/the-c...
    Thanks to everyone who has sent in history about this regex. Seems it was written ≥25 years ago by a Perl programmer named Abigail.
    Cheers to viewer Dave Cross who found this earliest-known mention in a 2000 blog post: test.neilk.net/...
    Thanks to viewers Chris Lawrence and Jimmy Diep for suggesting the topic.
    Huge thanks to my Patreon supporters. They keep me supplied with all the primes I need. / standupmaths
    CORRECTIONS
    Several people have corrected me that regex is zero indexed it’s just that \0 refers to the entire matched string.
    Mike Salisbury ands others have pointed out that the left-most column in the table of repeated wild cards shouldn't be included. Otherwise the length of the string could match a single prime length.
    At 6:07 I say "Begins and end with an m" when I meant ends with an “s”. No one has corrected that mistake with more vigour than viewer Timur Sultanov.
    There is some concern about my pronunciation of rejex.
    Let me know if you spot anything else!
    Filming, VFX and editing by Alex Genn-Bash
    Written and performed by Matt Parker
    Extra material by Sam Hartburn
    Number yeeting by Lucie Green
    Spooky lighting and producing by Nicole Jacobus
    Music by Howard Carter
    Design by Simon Wright and Adam Robinson
    MATT PARKER: Stand-up Mathematician
    Website: standupmaths.com/

КОМЕНТАРІ • 2,2 тис.

  • @standupmaths
    @standupmaths  Місяць тому +467

    Take your personal data back with Incogni! Use code standupmaths at the link below and get 60% off an annual plan: incogni.com/standupmaths
    Don’t use code ^.?$|^(..+?)\1+$.

  • @Cmanorange
    @Cmanorange Місяць тому +3731

    wow, what a neat trick! i'm adding this to my production code immediately, good luck new hires!

    • @omnijack
      @omnijack Місяць тому +264

      You monster

    • @OverkillDM
      @OverkillDM Місяць тому +85

      @@omnijack ‘Tis the season

    • @MichaelOfRohan
      @MichaelOfRohan Місяць тому +21

      YOURE why my neck hurts!! ='(

    • @robertdascoli949
      @robertdascoli949 Місяць тому +236

      make sure to comment
      "// not sure what this does but the system breaks if you remove it"

    • @ngwoo
      @ngwoo Місяць тому +8

      Halloween post

  • @Graphene_314
    @Graphene_314 Місяць тому +3984

    The plural of regex is regrets.

    • @hgiusdfajgfds
      @hgiusdfajgfds Місяць тому +153

      strangely enough, also the singular

    • @Bennici
      @Bennici Місяць тому +183

      "I have a problem. Oh, I know, I'll use regex to solve that problem." [...] "Now I have two problems."

    • @JPBelanger
      @JPBelanger Місяць тому +26

      To many IT/Prog guys here. 😁
      That said, pretty solid explanation by Matt, but yeah, pretty easy to get lost in RE

    • @lox7182
      @lox7182 Місяць тому +8

      @@JPBelanger is that really a surprise?

    • @JPBelanger
      @JPBelanger Місяць тому +5

      @lox7182 not really😁
      Guessing not many strangers to twenty sided die, board games, and LotR either 😁

  • @Yogarine
    @Yogarine Місяць тому +3380

    Regular expressions are already scary by nature. Making one that produces primes is truly terrifying.

    • @GustvandeWal
      @GustvandeWal Місяць тому +158

      Checks for*
      It does not produce them

    • @minamagdy4126
      @minamagdy4126 Місяць тому +77

      Also, this isn't a true regex. The type of self referentialism in action here is imopssible in simple regex's.

    • @Kosmokraton
      @Kosmokraton Місяць тому +54

      ​@GustvandeWal True, but just hook it up to an incrementing int and a while loop and you've got yourself a generator.
      (Or abuse a for loop, lol.)

    • @Varksterable
      @Varksterable Місяць тому +23

      ​@Kosmokraton I did think Matt was going to add this to his code.
      But on reflection, it's probably a good thing he didn't.
      Code like that is truely terrifying.
      Perl has a reputation of being a "write only language."
      Then regexes must be the "write only, and get it right only occasionally by fluke or trial and error API of coding."

    • @Varksterable
      @Varksterable Місяць тому +38

      ​@@minamagdy4126So only "simple" regexes are "true" regexes?
      How does that work?

  • @fgvcosmic6752
    @fgvcosmic6752 Місяць тому +609

    It really works! I put it on the extra notes section of my Amazon delivery, and it became Prime!

    • @colmx8441
      @colmx8441 Місяць тому +53

      I forgot the not and my parcel came chopped up into different parts.

    • @FirstLast-gw5mg
      @FirstLast-gw5mg Місяць тому

      @@colmx8441 Should've used ^(?!.?$|(..+?)\1+$) instead.

    • @Frexuz
      @Frexuz Місяць тому +7

      😂

    • @Celebration-p3u
      @Celebration-p3u Місяць тому +2

      Haha lemme try it-

    • @leap123_
      @leap123_ Місяць тому

      Tried it on my AliExpress delivery and it became Prime the drink. It tastes awful.
      My doctor also said my body have lead in them.

  • @scottieapplseed
    @scottieapplseed Місяць тому +173

    I loved the home joke at the end; you're such a good localhost.

    • @MrSonny6155
      @MrSonny6155 Місяць тому +11

      I tried the second incantation myself, but I just got sent to the party just down the road. Maybe I should have just used "~"...

    • @MykTaylor
      @MykTaylor Місяць тому +8

      ​@@MrSonny6155 it's cool that your neighborhood has a designated local host

  • @busyfreeguy
    @busyfreeguy Місяць тому +805

    15+ years of programming experience including using regular expressions and I still watched and enjoyed this video. It's a testament to Matt's enthusiasm and his skill as a speaker/teacher.

    • @paulwomack5866
      @paulwomack5866 Місяць тому +14

      Retired life long professional Unix user - Perl and Vi(m) mean regex is my native tongue!

    • @skylark.kraken
      @skylark.kraken Місяць тому +9

      Same, I figure out how it worked by just reading it, but he’s a joy to watch. Although, granted tapping on the video I was confused how it would be able to parse “17” as a prime and took a re-read of the regex to understand that it’s a length of the same character

    • @SuperHansburger93
      @SuperHansburger93 Місяць тому +1

      Same here. That's a really neat way to use regex. Not as efficient as the sieve of Eratosthenes, for the reasons mentioned at 14:30, but still really cool :)

    • @amits4744
      @amits4744 Місяць тому

      Which Python editor/IDE is this

    • @skylark.kraken
      @skylark.kraken Місяць тому

      @@amits4744 Matt is using VSCode

  • @tempest_dawn
    @tempest_dawn Місяць тому +1512

    love that the halloween horror episode on a math channel is . . . code

    • @maskettaman1488
      @maskettaman1488 Місяць тому +71

      Great idea for the next horror video. Simply presenting samples of hacked together python code from past videos

    • @minamagdy4126
      @minamagdy4126 Місяць тому +50

      No, the real horror would be ultra-optimized C++ code. The badly-written python code is a staple

    • @Appalachian7922
      @Appalachian7922 Місяць тому +41

      Nothing scarier than regular expressions.

    • @EarendilStar
      @EarendilStar Місяць тому +10

      But it's code that software engineers hate :)

    • @AdamMansbridge
      @AdamMansbridge Місяць тому +1

      And a prime-al forest and a computer joke

  • @RMDragon3
    @RMDragon3 Місяць тому +183

    To simplify, this takes the number and expresses it as a unary numeral system, where the number of marks is the value of the number you put in (e.g. 1 is 1, 2 is 11, 3 is 111, ...). The regex then looks to divide the unary representation into exactly N groups of size M, where both N and M are natural numbers with value 2 or larger. For example, you can divide 4 (represented as 1111) into 2 groups of "11". You can divide 6 (represented 111111) into 2 groups of "111" or 3 groups of "11". However, you can't divide 3 (represented as 111) into groups of the same size (technically you can do 3 groups of "1", but then M isn't 2 or larger). Basically, you are checking if the number has any factors bigger than 1, which obviously is only false for prime numbers.

    • @dudicrous
      @dudicrous Місяць тому +1

      I think you mean N and M are 2 or bigger (not "bigger than 2").

    • @dudicrous
      @dudicrous Місяць тому

      Still, I get why M should be 2 or bigger ( because the first dot in [..+?] is obligatory and the + means at least 1 extra. I don't get why N should be at least 2. The + after the group means 1 group or more doesn't it? 1 group of three dots shouldn't render True however.

    • @RMDragon3
      @RMDragon3 Місяць тому +5

      @@dudicrous oops, yes I do, fixed it now.
      N must be 2 or larger because the part in the parenthesis needs to match something (the first group), and the \1+ means that the same thing must appear at least one more time. The parenthesis part also "consumes" whatever it matches. So basically 4 (aka 1111) would match 11 with the (..+?) and the remaining 11 would match the \1+. If you have 2 (aka 11) you can match the parenthesis, but then you have nothing left to match the \1+ part.

    • @dudicrous
      @dudicrous Місяць тому +4

      @@RMDragon3 Ah yes, so ".+" is different from "(.)\1+". Looking back, Matt mentions it correctly, the video shows an erroneous first "or" though.

    • @acasualviewer5861
      @acasualviewer5861 Місяць тому +3

      I'm trying to figure out if the algorithm is quadratic or exponential
      I'd guess it's at least pseudo-exponential because the length of the number is n=LogN.. But this algorithm is N*N.
      Since LogN^b = N. Then the algorithm is O(n^b*N) = O(n^2b). Which is very big.
      Also for huge primes the O(N) memory requirement could be prohibitive.

  • @sillybear25
    @sillybear25 Місяць тому +50

    A minor bit of pedantry: ^.?$|^(..+?)\1+$ is a "regex" (i.e. a pattern specification understood by most common implementations of regular-expression-based pattern-matching engines), but it is not a regular expression in the strict sense of the term. The minimal definition of a strict regular expression includes only literal characters, a symbol standing for an empty string (typically ε), parentheses to clarify the order of operations, the alternation operator (vertical bar), and the Kleene star (asterisk). Most of the other symbols in our prime-matching regex can be derived from those in the minimal definition: The wildcard . is shorthand for (a|b|c|d|...), and a+ is shorthand for aa*. The symbols ^, $, and ? are irrelevant in a strict regular expression, since it either matches the entire string or it doesn't match at all. The real problem is the \1: There's no way to construct an equivalent out of the minimal definition.

    • @TheRyulord
      @TheRyulord Місяць тому +15

      Yup. Most modern "regex" engines are actually context-free grammar engines but they use syntax similar to true regex engines from decades past so people keep calling them that.

    • @flyinhigh7681
      @flyinhigh7681 Місяць тому +9

      Thank you for this comment! As someone who spends a good bit of time in theoretical computer science land it always bugs me when "regex" arent actually regular at all. Saved me the trouble of writing this comment myself

    • @yash1152
      @yash1152 18 днів тому +1

      thank you @TheRyulord for mentioning that the relation to CFG. i think it's something even more sinister... 'cz whereas a CFG/PDA uses stack, i.e. single time contiguous use, the backref uses arbitrary memory. & i dont remember which Grammar represents automaton with arbitrary append-only (say immutable read/write) memory.

    • @charlesstaats9902
      @charlesstaats9902 4 дні тому

      Google’s regex library, called RE2, does *not* allow backreferences like this since they can cause a regex search to take exponential time.

  • @tonicblue
    @tonicblue Місяць тому +15

    I love regular expressions. The xkcd is true, you really do feel like you've developed a super power when you master them

    • @nyankers
      @nyankers Місяць тому +2

      It's like actual wizardry, and no less arcane. Reading someone else's regex really is like deciphering a spell comprising ancient runes you individually understand...

  • @aeroeng15
    @aeroeng15 Місяць тому +471

    To clarify: a '?' on it's own matches 0 or 1 of the preceding character. A '?' following '+' modifies the greedy behavior of '+' to be less greedy

    • @DCSWCCkingpin1
      @DCSWCCkingpin1 Місяць тому +39

      Knows the different flavors of ? but doesn't know the difference between its and it's

    • @thatphatbaby
      @thatphatbaby Місяць тому +174

      @@DCSWCCkingpin1we’re programmers. Not languagers.

    • @DeronMeranda
      @DeronMeranda Місяць тому +174

      @@DCSWCCkingpin1 it'?s

    • @Lord_zeel
      @Lord_zeel Місяць тому +5

      @@DeronMeranda I see what you did there.

    • @lockaltube
      @lockaltube Місяць тому +23

      Just a note, what you call "less greedy" is known as lazy.

  • @mckseal
    @mckseal Місяць тому +1073

    Regex is already halloween worthy.

    • @nburakovsky
      @nburakovsky Місяць тому

      use regex all the time now to validate llm output formats, they arent scary they are lovely

    • @aikumaDK
      @aikumaDK Місяць тому +2

      It's the blackest of black magic

    • @Swordfish42
      @Swordfish42 Місяць тому +1

      ​@@aikumaDKOh yeah? Have you tried PERL?

    • @Talderas
      @Talderas Місяць тому +2

      ​​@@Swordfish42 RegEx inside Perl. The darkest of black magic.

    • @Mr_Yod
      @Mr_Yod Місяць тому

      @@Talderas RegEx inside Malbolge: try that, if you are brave enough! =)

  • @nickalasmontano1496
    @nickalasmontano1496 Місяць тому +96

    The cinematography of some of the more recent videos has been astounding. Nice work!

    • @kapriolenpfeifer
      @kapriolenpfeifer Місяць тому

      Indeed! The only minor point is that the editor should use a higher brightness or a screen with wider contrast.

  • @tostadojen
    @tostadojen Місяць тому +20

    *Matt:* "What the factor?"
    *Primes:* "Your factors can't help you here."

  • @_ax1ss
    @_ax1ss Місяць тому +19

    I've been writing code professionally for 20 years and this is the best explanation of regex I've seen. Great job!

    • @RobloxPrompt
      @RobloxPrompt Місяць тому +1

      At first I thought the ? meant unknown quantity before watching the video lol.

  • @HugoBDesigner
    @HugoBDesigner Місяць тому +227

    As a Regex connoisseur, I was really confused as to how the expression could possibly do that. But it makes perfect sense now. So simple, and yet so clever!

    • @WoolyCow
      @WoolyCow Місяць тому +28

      nobody is a regex connoisseur. nobody. it is where happiness goes to die...

    • @HugoBDesigner
      @HugoBDesigner Місяць тому +39

      @@WoolyCow Did you know that there exists a Regex Crossword puzzle game? It's surprisingly fun!

    • @I.____.....__...__
      @I.____.....__...__ Місяць тому +8

      @@WoolyCow Maybe for you, but I married RegEx and had two kids with it.

    • @VoidEternal6644
      @VoidEternal6644 Місяць тому +2

      @@HugoBDesigner WHERE?? IT DOES SOUND FUN I WANNA TRY IT /silly

    • @IceMetalPunk
      @IceMetalPunk Місяць тому +9

      @@WoolyCow Incorrect. I find RegEx quite fun and interesting. Figuring out the RegEx you need for a specific task is like solving a puzzle.

  • @arthurmesh7884
    @arthurmesh7884 Місяць тому +496

    Someone has to say it. Regular expressions,in their truest sense, ie ones that are equivalent to regular languages are not capable of primality test. Only extended ones that have “memory” can do it. I.e \1 part of the example above is what’s not possible in regular languages

    • @ModusTrollens91
      @ModusTrollens91 Місяць тому +116

      This brought me flashbacks having to prove that on an exam with the pumping lemma

    • @infernape716
      @infernape716 Місяць тому +12

      @@ModusTrollens91 *shudders*

    • @UJ-nt5oo
      @UJ-nt5oo Місяць тому +34

      @@ModusTrollens91 "prove that on an exam". username checks out

    • @glowingfatedie
      @glowingfatedie Місяць тому +13

      I'm not sure what you mean by "truest sense." The sense you gave is wrong - regular expressions aren't /equivalent to/ regular languages, they /describe/ regular languages. Backreferences add the ability to also describe non-regular languages, but that doesn't make such a regular expression implementation somehow be not a regular expression implementation.

    • @UJ-nt5oo
      @UJ-nt5oo Місяць тому +38

      ​@@glowingfatedienot sure thats right. regular expressions / regular languages etc can't do prime testing because they by definitin be matched with/reduced to a finite state machine which can't do counting. ie unbounded memory ie not finite i think we are just being too pedantic about the word regular tbh.

  • @Rohanology27
    @Rohanology27 Місяць тому +695

    What in the ^.?$|^(..?)\1+$ did I just watch?

    • @lockaltube
      @lockaltube Місяць тому +43

      Now it won't work! without +, ..? captures one or two ones, so magic stops after 1111. You gotta be lazy!

    • @alexandermcclure6185
      @alexandermcclure6185 Місяць тому +3

      Oh, it was 179, AKA p[41].

    • @RainBoxRed
      @RainBoxRed Місяць тому +12

      It's pronounced "factor".

    • @Luni_2000
      @Luni_2000 Місяць тому +1

      ​@@lockaltubeactually it will now only say true for multiples of 1 and 2, which is all the numbers

    • @AlmondAxis987
      @AlmondAxis987 Місяць тому +2

      This just tests for odd numbers greater than 1.

  • @ThePoxun
    @ThePoxun Місяць тому +5

    you know its going to be a good day when Matt releases a video that intersects with my most used number sets and my most used programming feature.

  • @austinwright2591
    @austinwright2591 Місяць тому +6

    13:48 This is not technically a "regular" expression because backreferences are not regular; as what the backreference matches changes based on previous input, and regular expressions are context-free (you can concatenate two regular expressions and it has the expected effect, but this does not hold true if the expression contains a backreference). "Regular" is an important property because it guarantees performance within a fixed amount of memory regardless of the input size, and compute time proportional to the input size, but the backreference obliterates that characteristic.

  • @stephenj9470
    @stephenj9470 Місяць тому +140

    3:31 The ability of Matt to accurately point to symbols that he'll put in later...

    • @mattparker-2
      @mattparker-2 Місяць тому +8

      it was seriously impressive. i wonder if it was first try

    • @HenryLoenwind
      @HenryLoenwind Місяць тому +12

      Not so impressive when you realise he's looking at a monitor showing a life feed from the camera. Easy to mark the right positions on that...

    • @stephenj9470
      @stephenj9470 Місяць тому +22

      @@HenryLoenwind Still tough to nail the pointing.

    • @WJS774
      @WJS774 Місяць тому +29

      @@HenryLoenwind Have you ever tried doing that? It is _not_ easy. Our brains did not evolve to process third-person feedback like that, so unless you have quite a bit of practice, you will need to do a lot of adjusting after your initial guess.

    • @j0code
      @j0code Місяць тому +6

      @@WJS774 Unless the camera feed is mirrored. Then it's pretty easy.

  • @masterandexpert288
    @masterandexpert288 Місяць тому +82

    "What the factor" got me hahaha

  • @KnightTobyas
    @KnightTobyas Місяць тому +388

    A bit pedantic, but 127.0.0.1 is a loopback address. It's like stepping outside to ring the doorbell to make sure it is working. The only time it sends you home is if you are already home.

    • @JdeBP
      @JdeBP Місяць тому

      The correct incantations would indeed be either "Set-Location -LiteralPath $env:USERPROFILE" or "cd" . (-:

    • @RobinSyl
      @RobinSyl Місяць тому +35

      The doorbell thing is how I'm gonna explain loopback from now on

    • @vl4dl3n
      @vl4dl3n Місяць тому +21

      "stepping outside", its more like trying to reach doorbell while standing inside :D

    • @ShadowManceri
      @ShadowManceri Місяць тому +3

      Or like if you would have portal gun then it makes the blue and orange portals the same.

    • @MonzennCarloMallari
      @MonzennCarloMallari Місяць тому +17

      "The only time it sends you home is if you are already home"
      Well that was oddly poetic

  • @rlarsen000
    @rlarsen000 Місяць тому +1

    After spending 52 years of my life coding, this is the first time any bit of code made me laugh. Good thing I had put my coffee down first. Great video!

  • @dalewheat
    @dalewheat Місяць тому +7

    Thank you, Matt, for reminding me how I truly feel about regular expressions. On an unrelated note, beware of “clever” code. I read that in a Fortran book once [citation needed].

    • @swankeepers
      @swankeepers Місяць тому

      You want "clever" code? Check out the International Obfuscated C Code contest (hosted for many years by a fellow that worked for me, who (non-ironically) is a famous prime-hunter.)

  • @stoopidgenious
    @stoopidgenious Місяць тому +114

    i love matts videos
    maths videos are the best

    • @nanamacapagal8342
      @nanamacapagal8342 Місяць тому +16

      import re
      comment = input()
      print(re.match(r'm...s',comment))
      >>> True

    • @Celebration-p3u
      @Celebration-p3u Місяць тому +2

      import re
      comment = input()
      print(re.match(r'm...s',comment))
      >>>True

    • @ssdd28561
      @ssdd28561 Місяць тому +2

      Oh, it's nice to see a totally normal person saying a totally normal sentence in the wild!

  • @CheaterCodes
    @CheaterCodes Місяць тому +1139

    just to be that guy: 127.0.0.1 isn't "home", it's loopback, so it should just send you back to where you're at right now.

    • @thepython10110
      @thepython10110 Місяць тому +243

      If you really want home, use ~

    • @mystifoxtech
      @mystifoxtech Місяць тому +91

      thanks for being that guy

    • @GrouchierThanThou
      @GrouchierThanThou Місяць тому +102

      ​@@thepython10110 That just translates (or expands as shell nerds like to say) to home. If you actually want to go home you should use cd.

    • @theeternalsw0rd
      @theeternalsw0rd Місяць тому +109

      just to be that more annoying guy. Um actually, it's technically the default loopback. You can add more manually and some operating systems support more out of the box. Any ip address in the subnet 127/8 is available for use as loopback.

    • @mineton1293
      @mineton1293 Місяць тому +52

      I love all the other "that guy"s replying to this

  • @CurtisDyer
    @CurtisDyer Місяць тому +58

    This looks like an alternate version of Abigail's prime regex that was posted on a Perl newsgroup in the '90s. Legendary Perl hacker.

    • @MishaTheElder
      @MishaTheElder Місяць тому +10

      Right. There should be an entire episode on Abigail's tricks

    • @ville_syrjala
      @ville_syrjala Місяць тому +1

      @@MishaTheElder Sounds like an episode of the "The Scary Door".

  • @musicdudejoe263
    @musicdudejoe263 Місяць тому +1

    This was your silliest video yet and I loved it, haha. Was cracking up at the thought of someone chasing you round a wood throwing numbers at you while filming it.

  • @michellevanallen3286
    @michellevanallen3286 Місяць тому +1

    My 8 year old loves your videos…I predict he will giggle uncontrollably anytime a new number is summoned but also give me a genuine look of confusion when trying to understand regex.
    And I wouldn’t be completely mad if he picks up on “what the factor” because that’s freaking hilarious but I still wouldn’t want to have to explain it to his teachers. 😂

  • @CoolAsFreya
    @CoolAsFreya Місяць тому +113

    There's no place like 127.0.0.1 ... except the rest of the /8 block of 16,777,216 addresses also reserved for loopback

    • @martijnvds
      @martijnvds Місяць тому +18

      And ::1

    • @runed0s86
      @runed0s86 Місяць тому

      ​@@martijnvdsthat's just 127.0.0.1 in ipv6

  • @estivalbloom
    @estivalbloom Місяць тому +297

    13:45 Hey! Regex capture groups *are* zero-indexed; the brackets start at one but capture group zero is the entire match. Don't you slander regular expressions by calling them one-indexed

    • @mouykaing6483
      @mouykaing6483 Місяць тому +49

      They're Parker-one-indexed

    • @mina86
      @mina86 Місяць тому +12

      No. The whole match is not a capture group. You can observe it by doing ‘re.search('bar', 'foobarbaz').groups()` which returns an empty tuple because there are no capture groups. \0 is the syntax to refer to the whole match.
      where `n` is non-zero digit is a syntax to refer to 1-indexed capture group.

    • @giacomostevanato2203
      @giacomostevanato2203 Місяць тому +20

      ​@@mina86 No
      is syntax for the nth backreference. It just so happen that the 0th backreference is the whole match and the (n+1)th backreference is the nth group. Groups by themselves are not 1-indexes, that only seem to happen when referring to them using backreferences because backreferences are not just groups.

    • @androlsaibot
      @androlsaibot Місяць тому +3

      @@giacomostevanato2203 So you're saying groups are not indexed at all because you reference the backreference and backreference \1 is the "first" (in a normal language sense) or "0th" (in a fictitious 0-indexed sense) group.

    • @giacomostevanato2203
      @giacomostevanato2203 Місяць тому +5

      @@androlsaibot I mean, in the 0-indexed list of backreferences, the one at index 1 is the first that is also a group (and is followed by the other groups).

  • @IsYitzach
    @IsYitzach Місяць тому +67

    Its not quite the Sieve of Eratosthenes as it checks if a the target number is a factor of all numbers smaller than it. The Sieve, as written by Eratosthenes, will only use prime numbers up the to the square root of the number as it will discard all composites before they are used.

    • @arirahikkala
      @arirahikkala Місяць тому +8

      I believe that's still trial division, not the actual sieve. See Melissa E. O’Neill's The Genuine Sieve of Eratosthenes, which goes into detail on this and derives asymptotics for both: The sieve does a lot less work to find all primes up to n than trial division, even trial division only checking prime numbers up to sqrt(n).

    • @theaxer3751
      @theaxer3751 Місяць тому +1

      I still haven't figured out how to do that one in Human Resource Machine optimally

    • @framegrace1
      @framegrace1 Місяць тому +3

      Original algorithm, as writen by Eratostenes, doesn't stop at sqrt n. It doesn't change the complexity, so it doesn't really matter, in fact.
      For him would have been a strange "optimization", as very few integers have rational square roots, an calculating the rest would be almost as tedious as the siege itself.

    • @kyay10
      @kyay10 Місяць тому +1

      ​@@framegrace1I don't think he would've been that confused by the idea of taking the ceiling of the square root. You can easily describe what that means in the language of geometry, which he definitely understood

    • @huellenoperator
      @huellenoperator Місяць тому +5

      @@framegrace1 You don't need to know roots, just stop when the square of the current number exceeds your chosen max.

  • @BrandonMeyer1641
    @BrandonMeyer1641 Місяць тому

    I stumbled upon your rgb Christmas tree and thought that was cool. So I looked into your Channel more. As someone who’s been learning r and wrangling data I was instantly intrigued. I was like, “is that a regular expression? Generate primes? It can’t be”.
    Subscribed.

  • @stigcc
    @stigcc Місяць тому +2

    In essence, this regex is a creative way to test the indivisibility property of prime numbers using string patterns. It’s a fascinating example of how regular expressions can be applied beyond their usual text-processing tasks!

  • @saFubar
    @saFubar Місяць тому +108

    For anyone else who like me was confused at 14:20, when Matt says "we can have multiples of them" he's referring just to the \1+ portion of the expression. This is in addition to the preceding capture group that it references, which in effect means that we *must* have multiples of them when taken across the whole string -- thus ensuring that prime numbers don't themselves get "factored" as p*1 and matched by the regex. This is more obvious when he says "you can have two twos, or three twos, or four twos, all the way up" even though the graphic makes it look like one two is an option.

    • @fradinetienne712
      @fradinetienne712 Місяць тому +3

      Thanks, I was so confused by how prime were not flagged as well!

    • @theaxer3751
      @theaxer3751 Місяць тому +1

      Thanks. I've worked with regex, but never \1 inside the regex. This actually makes sense to me now, whereas I was confused by Matt's phrasing.
      It's literally like 'insert whatever group 1 matched here'

    • @linazso
      @linazso Місяць тому

      That was confusing to me as well! Not sure I now fully understood how it does that but at least I got that it's somehow only referring to two or more groups.

    • @HenryLoenwind
      @HenryLoenwind Місяць тому +2

      Or, to say it in other words: The second part of regex grabs any number that's 2 or higher that is repeated 2 or more times. So if it can be expressed as "[2,3,4,...] x [2,3,4,...]", it matches.

    • @rmsgrey
      @rmsgrey Місяць тому +3

      Yeah, despite the first column of "or"s, the regex is "find something that matches what's in the brackets, and then find that exact string again one or more times" so if the bit in the brackets found "11", then the regex would be looking for "11" followed by at least one "11", taking up the entire string.

  • @krissp8712
    @krissp8712 Місяць тому +29

    This is approaching the level of LLM powered IsEven

    • @DanielQRT
      @DanielQRT Місяць тому

      it it orders of magnitude more efficient, this regex can check all numbers up to ~10_000 in ~3 seconds on my machine (using the fancy_regex crate in rust)

  • @kingbeauregard
    @kingbeauregard Місяць тому +79

    I was baffled until you pointed out that what we're really regex-ing against is a sequence of 1's. Regex is just trying to see if it can break that string of 1's into a number of equal-sized chunks (that are of length 2 or greater); for example, it could break "1111" into two chunks of length two, but it could not do anything similar with "11111".

    • @backwashjoe7864
      @backwashjoe7864 Місяць тому +10

      Thank you! He left out that kind of nice example and left me confused.

    • @manlyadvice1789
      @manlyadvice1789 Місяць тому +10

      Same here. I was baffled before, aghast after. It's as if someone was trying to come up with the least efficient, most memory-intensive prime-seeking method possible.

    • @skuizhopatt5318
      @skuizhopatt5318 Місяць тому

      Yeah, it's not JS hyere, so '1' != 1 ^^
      (Killing my own joke, but JS typing system is really bloated. Not to that point, though)

    • @theairaccumulator7144
      @theairaccumulator7144 Місяць тому

      @@manlyadvice1789 tbh it only takes pcre2 860 microseconds on my computer to test 1001 in 1468 steps. 3089 is tested to be prime in 3.52ms and 25310 steps. I've had regexes used in production take more steps.

    • @FirstLast-gw5mg
      @FirstLast-gw5mg Місяць тому

      Yeah, I was immediately proving it false by counter-example until he explained that 1) it's checking the length of the string, not the contents and 2) it's the opposite, it's checking for composite numbers.
      If you want prime lengths, use this instead:
      ^(?!.?$|(..+?)\1+$)

  • @Thewinner312
    @Thewinner312 Місяць тому +7

    A string is a "string of characters". It makes sense to say because it applies to all strings, not just those that also happen to be grammatically correct sentences. For example "^.?$|^(..+?)\1+$" is a string, but certainly not a sentence.

    • @FirstLast-gw5mg
      @FirstLast-gw5mg Місяць тому +3

      "20 to life" is a string, a sentence, and a noun phrase.

  • @Slowphoton
    @Slowphoton Місяць тому +5

    This regular expression has been around for decades. Attributed to Abigail, a Dutch JAPH (just another Perl hacker). I hope YT will not eat my comment.

  • @Richardincancale
    @Richardincancale Місяць тому +13

    I liked that it checked the primality of a series of ‘1’ characters. It shows that prime numbers are not dependent on the base of the numbers, just the number of ‘things’ being tested

  • @LuxFerre4242
    @LuxFerre4242 Місяць тому +574

    If have a problem, and you try to use regex to solve it, you now have two problems.

    • @zeikjt
      @zeikjt Місяць тому +72

      (problems)+

    • @dimesio
      @dimesio Місяць тому

      @@zeikjt (problems)*

    • @roxas8999
      @roxas8999 Місяць тому +14

      I was sure somebody would have commented this, so I scrolled through a lot until I found this

    • @ken830
      @ken830 Місяць тому

      @@roxas8999 Me too... first thing I did was search for "problems" and found this comment. Oldie... but goodie...

    • @alvaroludolf
      @alvaroludolf Місяць тому

      Pff... coward.

  • @johnchessant3012
    @johnchessant3012 Місяць тому +131

    "for completeness, I will show you that this definitely does work in practice"
    Can confirm. I said the incantation aloud and a wild 163 appeared, what about you guys?

    • @cheeseburgermonkey7104
      @cheeseburgermonkey7104 Місяць тому +10

      The demonic power might be accessing your memories while the incantation progresses because I got 41,024,320 random numbers that I don't know what to do with now.

    • @skandragon586
      @skandragon586 Місяць тому +10

      i must have said it wrong... i got an 8

    • @colinmcconnell827
      @colinmcconnell827 Місяць тому +8

      An Amazon Prime delivery appeared.

    • @alexandermcclure6185
      @alexandermcclure6185 Місяць тому

      @@colinmcconnell827 can confirm, i was the package

    • @alexandermcclure6185
      @alexandermcclure6185 Місяць тому +5

      I tried it and I discovered a new programming language called C** what should i do!?

  • @TheMyx231
    @TheMyx231 Місяць тому

    I applaud your commitment to making regular expressions make sense.

  • @DirkieDurky
    @DirkieDurky Місяць тому

    As someone who understands regex I still didn't understand how it could produce primes. Was super interesting to learn how, and what an amazing bit at the end! Thanks for all the great content you provide 🙏❤

  • @MattSeremet
    @MattSeremet Місяць тому +7

    I'm proud I was able to learn regular expressions well enough to update a popular stack exchange answer that had sat for a decade with a tiny error in the explanation. Subtle and important.

    • @jonasbarka
      @jonasbarka Місяць тому +2

      I would be proud if I could post a question to Stack Overflow without it immediately being closed for one reason or another...

  • @althaz
    @althaz Місяць тому +38

    Dang, prime numbers *AND* regex? It must be my birthday!

  • @ryanthunder3247
    @ryanthunder3247 Місяць тому +12

    I am always so happy to see a stand-up maths video. The ending spoky bit was quite a fun touch 😁

  • @user-Tony-1812
    @user-Tony-1812 Місяць тому

    I love all your posts ever since I discovered "Festival of the Spoken Nerd" ( Iave all the DVDs 🥰) but this wone was special. It put a massive smile on my face, thank you.

  • @DanWills
    @DanWills Місяць тому

    Totally fascinating! I love regex and this is such a cool example! Thanks so much for documenting and explaining your expedition to the prime realm Matt!

  • @chemann2944
    @chemann2944 Місяць тому +15

    "What the factor!" , nice one Matt

  • @tygrataps
    @tygrataps Місяць тому +9

    The camera man never dies! I am so sharing this with my work group tomorrow.

    • @tygrataps
      @tygrataps Місяць тому

      They loved it btw!

  • @RussellBeattie
    @RussellBeattie Місяць тому +5

    It's a fundamental law of computer science that any sufficiently complex regular expression is, by definition, immutable code: It can only be written or re-written, never edited (or understood).

    • @robadams1645
      @robadams1645 Місяць тому +1

      But if you put a regex in your code without a comment explaining what it does, I WILL fail your pull request.

  • @benjaminsprung315
    @benjaminsprung315 Місяць тому

    Thank you Matt for this prodigious incantation unveiling the deep mystery of regular expressions!

  • @DAveShillito
    @DAveShillito Місяць тому +1

    One of my favourite quotes "If you have a problem that can be solved by regular expressions, you now have two problems" 😁

  • @lordterk
    @lordterk Місяць тому +145

    Screaming in regular expressions 😂

    • @Milamberinx
      @Milamberinx Місяць тому +1

      Careful, with good luck and bad luck it'll match, not necessarily the same or right things.

    • @lordterk
      @lordterk Місяць тому

      @Milamberinx hahahaha absolutely true! 🤣

    • @Duraludon884
      @Duraludon884 Місяць тому +7

      "A+"

  • @jamesmnguyen
    @jamesmnguyen Місяць тому +146

    Haven't watched the full video yet but I immediately said, "Now plug the largest Mersenne Prime into that regex"

    • @Z_Inspector
      @Z_Inspector Місяць тому +21

      I'm not quite sure python can handle a number of that size, but if it could, it would take an eternity to run anyway!

    • @MrKahrum
      @MrKahrum Місяць тому +23

      calculate it for me and i will ;)
      tl;dw: after two infinities, my computer spits out its answer, confirming that which we definitonally knew to be true. we look at each other, and say "nice".

    • @FScott-m1n
      @FScott-m1n Місяць тому +3

      Ka -- blooie!

    • @marcoottina654
      @marcoottina654 Місяць тому +5

      ​@@MrKahrum "Top long ; didn't ..... Write?"

    • @jamesmnguyen
      @jamesmnguyen Місяць тому +8

      @@marcoottina654 Too Long; Didn't Watch

  • @ErzengelDesLichtes
    @ErzengelDesLichtes Місяць тому +18

    The important part in cracking this is the text you’re running it on and what on earth ‘1’*n means in python. Once I figured out it means “repeat the character n times” and so you’re matching against a string of repeating characters, what the regex is doing became clear.

  • @electricketchup
    @electricketchup Місяць тому

    This is by far your best video yet. By the way, the second incantation can be simplified to the string "::1"

  • @peelaza
    @peelaza Місяць тому

    what an amazing cinematic treat at the end! thanks for the vid!

  • @youdontknowme5969
    @youdontknowme5969 Місяць тому +21

    Aaahh yes, RegEx's
    Fun to concoct
    Absolute nightmare to debug

    • @asandax6
      @asandax6 Місяць тому +2

      As someone who's written Regex for 2 years I still have no idea what I'm doing and I have a feeling I never will.

    • @ailaG
      @ailaG Місяць тому

      ​@@asandax6 that's okay, I've been doing them for 20 and I feel the same.
      At least we can now ask ChatGPT...
      One time ages ago someone asked in a local forum about a regex and I thought he was parodying them because on top of the whole cat-walked-on-keyboard mess it had smileys in it! (this is before emojis, but the image equivalent of a 😊 😢 etc)
      Until I realised the colons and brackets were part of the original regex, transformed by the forums software
      And while that doesn't demonstrate how annoying regex is, it sure shows it

  • @GWConsultant
    @GWConsultant Місяць тому +10

    IMHO @15:21 explanation of (..+)\1 in the picture is incorrect! For instance, (11)\1 shall NOT match 11 but shall match 1111 or 111111 because at least ONE REPETITION of the given group given in parentheses MUST be present! If there is no repetition of the given group, then there is no match!

    • @fatemonkey
      @fatemonkey Місяць тому

      There doesn't need to be a repitition. + matches 1 or more times, so it's checking if 11 appears 1 or more times, thus 11 would match...

    • @AbiGail-ok7fc
      @AbiGail-ok7fc Місяць тому +3

      @@fatemonkey 11 will not match. + matches indeed 1 or more times, but \1+ means that you have to match 1 or more times whatever was matched by the capture group *following* the match of the capture group.

  • @ChalkyWhiteChalkyWhite
    @ChalkyWhiteChalkyWhite Місяць тому +9

    'i love matts videos'

  • @AthenaAGT
    @AthenaAGT Місяць тому

    I’ve never been happier to be even slightly fluent in regex. It was torture to learn but this made it worth it.

  • @gmr7901
    @gmr7901 21 день тому +1

    17:25 Imagine just walking in the forest and watching some dude running out from the cameraman, who throwns at him 3D-printed digits...😅

  • @arc8dia
    @arc8dia Місяць тому +19

    The production value of this video is amazing ... for a math video

  • @benharri
    @benharri Місяць тому +28

    regex in UA-cam titles. coming back to this later 📌

  • @decare696
    @decare696 Місяць тому +33

    '^' is called a caret. An up-arrow would be ↑...

    • @JdeBP
      @JdeBP Місяць тому +6

      In the 7-bit world of the 1960s, they were the same thing. Have a look at the early days of ASCII. Terrible Python has yet to fully escape that world.

    • @tavern.keeper
      @tavern.keeper Місяць тому +1

      It's called a circumflex

    • @menachemsalomon
      @menachemsalomon Місяць тому +1

      Yes. The '^' is the caret, and the '|' is the stick.
      You know, "Do this, or else ..." That's a stick. And that's what '|' is used for, though usually doubled to accomplish that. `Do() || die("Hey, I've died twice.")` works in C, though it's a Perl idiom.

    • @FirstLast-gw5mg
      @FirstLast-gw5mg Місяць тому

      I prefer to think of it as a naked circumflex.

    • @埊
      @埊 Місяць тому

      @@menachemsalomon 丨 and 人 and 个 is used where?

  • @vacronda
    @vacronda Місяць тому

    This video's production value is like finding a new prime - astronomically impressive!

  • @WispYart
    @WispYart Місяць тому

    As a student who at the time give a lecture to the class on regex, I love this video, thank you Matt!

  • @Niveum
    @Niveum Місяць тому +8

    If we took the formal language theory definition of regular expressions (from the Chomsky hierarchy), evaluating primes should not be possible.
    Regex implementations (like in Python) uses backtracking and recursive matching.

  • @maertsnosmirc
    @maertsnosmirc Місяць тому +27

    I can think of nothing scarier than regular expressions

    • @FirstLast-gw5mg
      @FirstLast-gw5mg Місяць тому +1

      Well then you shouldn't be afraid of ^(?!.?$|(..+?)\1+$) since it's looking for the beginning of something that _isn't_ matching the regular expression.

  • @MadSpacePig
    @MadSpacePig Місяць тому +11

    I remember reading Humble Pi and near the end thinking 'Matt is really more of a Computer Scientist at this point rather than just a mathematician'
    I think this is the nail in the coffin.

    • @TheGreatAtario
      @TheGreatAtario Місяць тому +7

      No computer scientist would consider "sentence" to be the proper meaning of "string"

    • @swankeepers
      @swankeepers Місяць тому +1

      @@TheGreatAtario was going to post the same, but thanks for doing it first.

  • @newcantinacrispychickentac7754
    @newcantinacrispychickentac7754 Місяць тому

    As someone with no computer science knowledge, this video was very easy to follow. Great job!

  • @melthomas8048
    @melthomas8048 Місяць тому

    Not gonna lie, Business Matt was so good with the transition that I wasnt even skipping that Ad

  • @CaelVK
    @CaelVK Місяць тому +7

    regex is definitely one of the scariest things you can show to any programmer

  • @sevcoyote4730
    @sevcoyote4730 Місяць тому +43

    I don't think I've ever heard somebody pronounce the 'g' in 'regex' like the 'g' in 'regular', even though it obviously makes sense when you think about it.

    • @thepython10110
      @thepython10110 Місяць тому +27

      I've always pronounced it that way in my head, and was surprised when I heard it the other way. It really is exactly the same as the GIF thing.

    • @JavedAlam-ce4mu
      @JavedAlam-ce4mu Місяць тому +11

      I have only ever heard it pronounced rejex. The sound from the reg in register. I think it's pronounced this way because it is more phonetically satisfying.

    • @thepython10110
      @thepython10110 Місяць тому +7

      @@JavedAlam-ce4mu That is the normal pronunciation, and makes sense in English (usually G before I or E is a soft G, like in other languages), but a hard G also makes sense because it comes from "reGular."

    • @grelca
      @grelca Місяць тому +2

      @@thepython10110​​⁠​⁠the folks who get mad when people say gif with a soft g would like a word with you 😂

    • @auralluring
      @auralluring Місяць тому +3

      i’ve heard it so many times both ways, at this point i’m not even sure which way i usually say it

  • @kingbeauregard
    @kingbeauregard Місяць тому +7

    Regular expressions are otherworldly. Do learn them if you do any programming, though; they are one of the most useful things you can master.

    • @mjkmetso2935
      @mjkmetso2935 Місяць тому +3

      They are also the easiest way to introduce massive bugs into production *Looking at crowdstrike*

    • @_Agent_86
      @_Agent_86 Місяць тому +1

      The most useful thing to master in coding is how to make the most readable code possible. In that light, regex is the least useful things you could master. Never be clever!

    • @kingbeauregard
      @kingbeauregard Місяць тому +1

      @@_Agent_86 Yes and no. Yes on, readability is key to good code; code that is easy to maintain tends towards fewest bugs. No on your disdain for regular expressions: even simple regular expressions are useful as hell. For example, if you want to test the format of a positive integer with no leading zeros, it's /^[1-9]\d*$/ . That involves fewer gyrations than trying to evaluate the expression numerically and stripping off leading zeroes / a decimal / etc. Or trying to extract fields of data from a string, regular expressions can make difficult tasks very simple.
      You're right that regular expressions can be abused, to which I say: don't abuse them. Problem solved.

    • @kingbeauregard
      @kingbeauregard Місяць тому +1

      @@mjkmetso2935 Even that isn't the fault of regex. The incident report identifies this as the problem: "The content validator evaluated the new template instances under the assumption that the IPC template type would provide all 21 inputs. Due to the mismatch, the validator failed, leading to the incident." It wasn't a regex blunder or a bug in regex or an ambiguity in regex; from what they're describing, the coder operated under incorrect assumptions about the data. The same error would have occurred with a non-regex validator.

    • @_Agent_86
      @_Agent_86 Місяць тому +2

      @@kingbeauregardI do agree, and I do use them, but they are inherently low readability. And when I review code with one, I assume it was copy pasted from somewhere. Then I have to divert and research carefully. My comment was mostly to quell the enthusiasm of the op a bit! Appreciate your POV though.

  • @Utoxin
    @Utoxin Місяць тому +2

    I've used regex for 25 years, and still didn't spot the trick until you started explaining the backreference magic. GAH.

  • @deanolium
    @deanolium Місяць тому

    Yay! Regex!!! Quite honestly one of my favourite things I learned at uni. Such a cool use of it, though it will eat up computer resources quite quickly :D

  • @ianmcdougall2898
    @ianmcdougall2898 Місяць тому +11

    There's no place like ::1...

    • @thepython10110
      @thepython10110 Місяць тому +12

      There's no place like ~

    • @skuizhopatt5318
      @skuizhopatt5318 Місяць тому

      Hey ! I'm your new postman. You can trustfully bring me all your mail, including valuables.
      (yes, this is an ipv6 joke too :p )

  • @kea2878
    @kea2878 Місяць тому +4

    Spooky that the QR code at 9:19 has a ghost in the middle.

  • @two_number_nines
    @two_number_nines Місяць тому +16

    13:57 no, the capture groups ARE zero-indexed. The \0 capture group is the whole regex pattern itself. You can't use the \0 capture group within the regex itself, but you can use it in re.sub(...) and re.findall(...).group(0).

    • @mina86
      @mina86 Місяць тому +5

      No. The whole match is not a capture group. You can observe it by doing ‘re.search('bar', 'foobarbaz').groups()` which returns an empty tuple because there are no capture groups. \0 is the syntax to refer to the whole match.
      where `n` is non-zero digit is a syntax to refer to 1-indexed capture group.

  • @nixel1324
    @nixel1324 Місяць тому +2

    16:40 I appreciate the factor joke in a video about primes.

  • @sheepphic
    @sheepphic Місяць тому +2

    This isn't actually the Sieve of Eratosthenes, it's just trial division. The thing that makes the SoE powerful is you don't ecer check crossed-out numbers, meaning you're only checking if *primes* are a factor of n, but this does no such thing, and so is much slower.

  • @JerryFlowersIII
    @JerryFlowersIII Місяць тому +7

    00:30 I like how you can see Matt's Matte.

  • @privacyvalued4134
    @privacyvalued4134 Місяць тому +7

    17:15 Who wants to play the Matt Parker platformer video game now?

    • @Saleca
      @Saleca Місяць тому

      Prime runner

  • @pg_pete
    @pg_pete Місяць тому +5

    Wildcards are OutOfMemoryExceptions waiting to happen

    • @nathanjohnson9715
      @nathanjohnson9715 Місяць тому +2

      True story! I'm a pentester, and one of the things we always look for is dangerous regex or "redos" vulnerabilities in code we're testing.

  • @EDoyl
    @EDoyl Місяць тому +1

    My favorite type of thing in the entire world is anything which is all three of:
    1) funny
    2) extremely clever
    3) extremely stupid

  • @nathanrogers7397
    @nathanrogers7397 Місяць тому

    This video was relevant to my interests both, as an amateur prime number hunter and as a person who uses regular expressions to manipulate text files as part of my job. Thanks for the fun video!

  • @arithex
    @arithex Місяць тому +6

    wow just 1 line of code! that must be really fast, right ... right?

    • @LexLissauer
      @LexLissauer Місяць тому

      😂
      It will be fast, as it is only applicable to relatively small numbers.

  • @jbrecken
    @jbrecken Місяць тому +9

    That scene in another dimension was right out of "Planet of the Prime Matts."

    • @denelson83
      @denelson83 Місяць тому +3

      Uh, 314159, as in asteroid 314159 Mattparker, is prime.

  • @Fabio292
    @Fabio292 Місяць тому +7

    As my high school programming teacher said: "If you have a problem and you want to solve it using regex, you now have two problems"

    • @FirstLast-gw5mg
      @FirstLast-gw5mg Місяць тому +1

      In this case, the second problem of getting the opposite of what you wanted could also be solved using regex.
      ^(?!.?$|(..+?)\1+$)

  • @linguica
    @linguica Місяць тому

    I love regular expressions. I taught myself to use them in college and then as an intern doing data entry I was able to complete a full day's "work" in like 30 minutes.

  • @thetaphi
    @thetaphi Місяць тому

    Someone had a looot of fun literally throwing numbers at you. Excellent film making.

  • @fishHater
    @fishHater Місяць тому +16

    Also did he just refer to our beloved pipe as vertical line

  • @blindsniper35
    @blindsniper35 Місяць тому +7

    REGEX for Halloween video. Yeah that tracks

  • @tetraquark4477
    @tetraquark4477 Місяць тому +8

    I haven't thought about REGEX in 10 years. Thanks for breaking my brain!

  • @shubhamg9495
    @shubhamg9495 Місяць тому

    Illya's blog post is fantastic!