#regexps — Public Fediverse posts

Empty matches in Python’s `re` module

https://blog.narf.ssji.net/2025/04/30/empty-matches-in-pythons-re-module/

Python’s `re.sub` method has a weird, though documented, behaviour.

Replacements for empty-matching patterns such as `/.*/` applied to a non-empty string will lead to two matches. The replacement will therefore be applied twice.

A simple fix is to make sure the pattern is not empty-matching, e.g. `/.+/`.

#debugging #Python #regexps #sed

Best answer on regexps ever? 🧐 😎

- What is the plural form of regex?

- If you've used more than one of them, you'll know that the plural of "regex" is "regrets." – cjs (Mar 14, 2022 at 23:46)

#regex #regexps #programmer #programming #devops #regularexpression

Extended #regexps are great for place names like "Wellesley" where you can not remember if it's Welesley, Welleseley, Wellesselley, Welleslley, or Welesslley to save your dadburn life. ;)

/wel+es+e?l+ey/ !!!

cc: @amin

@neustradamus #PCRE continues to be a misnomer; it’s a modified subset of #Perl #RegularExpressions with dozens of differences: https://pcre.org/current/doc/html/pcre2compat.html

It's not "(C)ompatible." Accept no substitutes: https://perldoc.perl.org/perlre

#PCRE2 #PerlIncompatibleRegularExpressions #RegularExpression #RegExes #RegExps #regex #regexp

@neustradamus #PCRE continues to be a misnomer; it’s a modified subset of #Perl #RegularExpressions with dozens of differences: https://pcre.org/current/doc/html/pcre2compat.html

It's not "(C)ompatible." Accept no substitutes: https://perldoc.perl.org/perlre

#PCRE2 #PerlIncompatibleRegularExpressions #RegularExpression #RegExes #RegExps #regex #regexp

@neustradamus #PCRE continues to be a misnomer; it’s a modified subset of #Perl #RegularExpressions with dozens of differences: https://pcre.org/current/doc/html/pcre2compat.html

It's not "(C)ompatible." Accept no substitutes: https://perldoc.perl.org/perlre

#PCRE2 #PerlIncompatibleRegularExpressions #RegularExpression #RegExes #RegExps #regex #regexp

@neustradamus #PCRE continues to be a misnomer; it’s a modified subset of #Perl #RegularExpressions with dozens of differences: https://pcre.org/current/doc/html/pcre2compat.html

It's not "(C)ompatible." Accept no substitutes: https://perldoc.perl.org/perlre

#PCRE2 #PerlIncompatibleRegularExpressions #RegularExpression #RegExes #RegExps #regex #regexp

@neustradamus #PCRE continues to be a misnomer; it’s a modified subset of #Perl #RegularExpressions with dozens of differences: https://pcre.org/current/doc/html/pcre2compat.html

It's not "(C)ompatible." Accept no substitutes: https://perldoc.perl.org/perlre

#PCRE2 #PerlIncompatibleRegularExpressions #RegularExpression #RegExes #RegExps #regex #regexp

@hschne I think a lot of folks know about it, but there aren't too many use cases in my own code where it isn't easier just to assign capture groups to variables post facto. Plus, I'm one of those people that think #regex is often abused when simple matches followed by code is better than really complicated #regexps.

Plus, "shiny and cool" isn't always better than readable, and named capture groups just hurt my eyes. 😎

Any #RakuLang core hackers want to take up this challenge?

#RegularExpressions #RegExps #RegExes #RegEx https://ruby.social/@gd/110718818730295923

@regehr @commodore @dev There is even a (low-severity, a/k/a “cruel”) #PerlCritic policy to discourage everything but $_, @_, $], and numbered #RegularExpression capture variables: https://metacpan.org/pod/Perl::Critic::Policy::Variables::ProhibitPunctuationVars

https://metacpan.org/pod/Perl::Critic::Policy::Variables::ProhibitMatchVars already protects you against the performance-sapping $`, $&, and $' match variables

And you can configure your own prohibited list with https://metacpan.org/pod/Perl::Critic::Policy::Variables::ProhibitEvilVariables

#Perl #RegEx #RegExp #RegExes #RegExps

Spent half a day polishing complex #regexps in #vim . And they work too, but perl has a little different standard, so I'm basically stuck in grep -p punching a file until it works. As they say in #taoup , sometimes you just have to brute force prototype. #unix #bashcore #hobbylinguist #hobbytranslator

Spent half a day polishing complex #regexps in #vim . And they work too, but perl has a little different standard, so I'm basically stuck in grep -p punching a file until it works. As they say in #taoup , sometimes you just have to brute force prototype. #unix #bashcore #hobbylinguist #hobbytranslator

Spent half a day polishing complex #regexps in #vim . And they work too, but perl has a little different standard, so I'm basically stuck in grep -p punching a file until it works. As they say in #taoup , sometimes you just have to brute force prototype. #unix #bashcore #hobbylinguist #hobbytranslator

Spent half a day polishing complex #regexps in #vim . And they work too, but perl has a little different standard, so I'm basically stuck in grep -p punching a file until it works. As they say in #taoup , sometimes you just have to brute force prototype. #unix #bashcore #hobbylinguist #hobbytranslator

Spent half a day polishing complex #regexps in #vim . And they work too, but perl has a little different standard, so I'm basically stuck in grep -p punching a file until it works. As they say in #taoup , sometimes you just have to brute force prototype. #unix #bashcore #hobbylinguist #hobbytranslator

@Codely @drupler It helps to build your complicated #RegularExpressions in pieces and store them in separate variables. You can then test them in isolation and not be confused when you concatenate them together for your actual matching.

Both #PHP and #JavaScript also support named capture groups if you’re doing replacements. They’re a lot more readable.

Also, PHP’s #PCRE-based engine has a PCRE_EXTENDED flag that lets you add whitespace, newlines, and comments.

#regexes #regexps

In the absence of #Mastodon #filter #regexps, my anti-twitter-RTs filter is now

twitter.com/

The trailing backslash catches links to tweets (twitter.com/screenname/12345 etc) but allows other mentions of twitter.com, e.g., a username.

@Perl Are you working through the #OReilly #book ‘Learning #Perl’? Get extra practice with co-author brian d foy’s ‘Learning Perl Exercises’ #ebook: https://leanpub.com/learning_perl_exercises

Don’t have ‘Learning Perl’ yet? Buy it in paperback or ebook here: https://shop.aer.io/oreilly/p/learning-perl-8th/9781492094951-9149
Prefer #Amazon #Kindle? https://amzn.to/3QZj7t6 (affiliate link)

#books #bookstodon #coding #programming #SoftwareDevelopment #ProgrammingLanguages #Perl5 #RegularExpressions #regexes #regexps #Unicode #CPAN

@sjn @cb 99% of the “#Perl is line noise” complaints are because of unformatted #RegularExpressions. Every language worth anything eventually supports them, but only @Perl (and #awk, earlier) makes them first-class citizens. And with Perl you can format and comment them for readability: https://perldoc.perl.org/perlretut#Embedding-comments-and-modifiers-in-a-regular-expression

We format the rest of our code for humans. Why not #regexps?

#PerlCritic can warn against bad regexps: https://metacpan.org/search?size=200&q=module%3APerl%3A%3ACritic%3A%3APolicy%3A%3ARegularExpressions

#regex #regexes #programming #coding #SoftwareDevelopment

@randomatic @[email protected] @HaplogroupNews @[email protected] A previous employer of mine used re::engine::RE2 for many things, because a) you can cap the memory usage to avoid #DoS attacks, and b) the lead developer was all about premature optimization. https://metacpan.org/pod/re::engine::RE2

But you can’t use the /x flag for better readability, and we ran into some nasty #Unicode bugs and had to fall back to regular Perl #RegExps in those cases.