4 ms·

What are your Ruby Regex Idioms?

30 points by rahulvohra 17y ago

sofal 17y ago
One of my favorite patterns: _, username, domain = */([^@]+)@(.+$)/.match("foo@example.com")
- lzell 17y ago
  Nice. I am intrigued by the leading underscore, are you just using that as a throwaway variable? You could get the username and domain on their own with: username, domain = [*/([^@]+)@(.+$)/.match("foo@example.com")][1..-1] And it is super readable.
  - twoism 17y ago
    this works as well... username,domain = */([^@]+)@(.+$)/.match("foo@example.com").captures
- jherdman 17y ago
  If you're capturing something you don't want, you can always prefix your match with '?:' to have a non-capturing group. FWIW, I personally prefer the #match method. Some of the examples in this article just make me want to hurt people. Especially usage of $1, $2, etc.
  - tierack 17y ago
    In that case, /([^@]+)@(.+$)/.match("foo@example.com")[0] returns the whole string matched by the expression, and [1] and [2] return the first and second groups. That's why the throwaway is there. To get rid of the throwaway, this is a possibility: username, domain = */([^@]+)@(.+$)/.match("foo@example.com").captures Of course, your string better match, otherwise you'll get a NoMethodError.
  - steveklabnik 17y ago
    $1 and $2 are probably still there do to Ruby's Perl heritage. I don't particularly mind their use, but that's probably due to my long history with Perl.
zzleeper 17y ago
Woah.. I want that for Python..
- jacobolus 17y ago
  I sure don’t. Putting a regular expression in a slice for a string runs totally counter to all existing python idioms, and would utterly confuse anyone trying to read the code. There are definitely other ways of accomplishing this with reasonably compact syntax that are also intuitive and clear. (But I'm unconvinced it needs special syntax at all. It saves a couple lines here and there, maybe, but at the cost of making the language more complex.) caller[0][/`([^']*)'/, 1] isn't really so much shorter than: re.search("`([^']*)'", caller[0]).group(1) and the latter is quite a bit more explicit.
  - emmett 17y ago
    Your code does not accomplish the required task. The goal is to return nil when there is no match, or the nth match if there is. >>> re.search('a(x)a', 'axa').group(1) 'x' >>> re.search('a(x)a', 'aya').group(1) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'NoneType' object has no attribute 'group' The idiomatic python for the job is: match = re.search("`([^']*)'", caller[0]) if match: match.group(1) else: None (or some nonsense involving try/except, which would be even worse).
    - jacobolus 17y ago
      Ah, you’re right. In many cases, I don’t want to return None when there’s no match, but for short scripts quickly tossed together, the extra few lines can be a bit annoying. try: re.search("`([^']*)'", caller[0]).group(1) except: None
  - samstokes 17y ago
    > I'm unconvinced it needs special syntax at all. What's interesting is that it's actually not special syntax - at least, it's not special syntax for regex usage. The syntax obj[arg, arg, arg] looks weird because in most languages things that look like subscripts can't have multiple arguments, but it's just sugar for the method call obj.[](arg, arg, arg), which is pretty mundane. The semantics are just the semantics of that method on the class of 'obj', and can therefore be defined in library or user code. Note I'm not defending the specific use of it here to write odd-looking regex code - I just think it's interesting that the language is flexible enough to allow that kind of usage without special-casing it. Raganwald wrote a blog post [1] along similar lines, arguing that it's a core part of Ruby's language philosophy, about this snippet: (1..100).inject(&:+) [1]: http://weblog.raganwald.com/2008/02/1100inject.html http://weblog.raganwald.com/2008/02/1100inject.html
nanijoe 17y ago
This (ruby) regex thing still gives me a headache , esp when I'm trying to figure out other people's code
- sh1mmer 17y ago
  I love regex, but man it's still crazy voodoo. I hope those lines were well commented.
- deleted 17y ago
  [deleted]
- carbon8 17y ago
  You can also use this as String#slice, which is a little clearer: "foo@example.com".slice(/@(.*)/, 1)
sant0sk1 17y ago
I use Rubular all the time for testing my regexes with ease. Give it a shot, its really well done: http://rubular.com/ http://rubular.com/
- samstokes 17y ago
  Looks like a useful tool. I've been using a similar one: http://regex.powertoy.org/ http://regex.powertoy.org/ The latter supports several languages' regex dialects, and I like the visual way it displays group matches, particularly when groups are nested. It can be a bit clunky, though, whereas Rubular is pretty clean and usable.
iamwil 17y ago
I didn't see it mentioned, but, btw, this code allows a method to introspect to figure out what the method name that's currently being executed. caller[0][/`([^']*)'/, 1] Note that you only need to do this for Ruby 1.8. In Ruby 1.9, there will be a __method__() and __callee__() method that does the same thing.
grandalf 17y ago
(foo){2,5}

30 points by rahulvohra 17y ago

sofal 17y ago

One of my favorite patterns: _, username, domain = */([^@]+)@(.+$)/.match("foo@example.com")

lzell 17y ago
Nice. I am intrigued by the leading underscore, are you just using that as a throwaway variable? You could get the username and domain on their own with: username, domain = [*/([^@]+)@(.+$)/.match("foo@example.com")][1..-1] And it is super readable.
- twoism 17y ago
  this works as well... username,domain = */([^@]+)@(.+$)/.match("foo@example.com").captures
jherdman 17y ago
If you're capturing something you don't want, you can always prefix your match with '?:' to have a non-capturing group. FWIW, I personally prefer the #match method. Some of the examples in this article just make me want to hurt people. Especially usage of $1, $2, etc.
- tierack 17y ago
  In that case, /([^@]+)@(.+$)/.match("foo@example.com")[0] returns the whole string matched by the expression, and [1] and [2] return the first and second groups. That's why the throwaway is there. To get rid of the throwaway, this is a possibility: username, domain = */([^@]+)@(.+$)/.match("foo@example.com").captures Of course, your string better match, otherwise you'll get a NoMethodError.
- steveklabnik 17y ago
  $1 and $2 are probably still there do to Ruby's Perl heritage. I don't particularly mind their use, but that's probably due to my long history with Perl.

zzleeper 17y ago

Woah.. I want that for Python..

jacobolus 17y ago
I sure don’t. Putting a regular expression in a slice for a string runs totally counter to all existing python idioms, and would utterly confuse anyone trying to read the code. There are definitely other ways of accomplishing this with reasonably compact syntax that are also intuitive and clear. (But I'm unconvinced it needs special syntax at all. It saves a couple lines here and there, maybe, but at the cost of making the language more complex.) caller[0][/`([^']*)'/, 1] isn't really so much shorter than: re.search("`([^']*)'", caller[0]).group(1) and the latter is quite a bit more explicit.
- emmett 17y ago
  Your code does not accomplish the required task. The goal is to return nil when there is no match, or the nth match if there is. >>> re.search('a(x)a', 'axa').group(1) 'x' >>> re.search('a(x)a', 'aya').group(1) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'NoneType' object has no attribute 'group' The idiomatic python for the job is: match = re.search("`([^']*)'", caller[0]) if match: match.group(1) else: None (or some nonsense involving try/except, which would be even worse).
  - jacobolus 17y ago
    Ah, you’re right. In many cases, I don’t want to return None when there’s no match, but for short scripts quickly tossed together, the extra few lines can be a bit annoying. try: re.search("`([^']*)'", caller[0]).group(1) except: None
- samstokes 17y ago
  > I'm unconvinced it needs special syntax at all. What's interesting is that it's actually not special syntax - at least, it's not special syntax for regex usage. The syntax obj[arg, arg, arg] looks weird because in most languages things that look like subscripts can't have multiple arguments, but it's just sugar for the method call obj.[](arg, arg, arg), which is pretty mundane. The semantics are just the semantics of that method on the class of 'obj', and can therefore be defined in library or user code. Note I'm not defending the specific use of it here to write odd-looking regex code - I just think it's interesting that the language is flexible enough to allow that kind of usage without special-casing it. Raganwald wrote a blog post [1] along similar lines, arguing that it's a core part of Ruby's language philosophy, about this snippet: (1..100).inject(&:+) [1]: http://weblog.raganwald.com/2008/02/1100inject.html http://weblog.raganwald.com/2008/02/1100inject.html

nanijoe 17y ago

This (ruby) regex thing still gives me a headache , esp when I'm trying to figure out other people's code

sh1mmer 17y ago
I love regex, but man it's still crazy voodoo. I hope those lines were well commented.
deleted 17y ago
[deleted]
carbon8 17y ago
You can also use this as String#slice, which is a little clearer: "foo@example.com".slice(/@(.*)/, 1)

sant0sk1 17y ago

I use Rubular all the time for testing my regexes with ease. Give it a shot, its really well done: http://rubular.com/ http://rubular.com/

samstokes 17y ago
Looks like a useful tool. I've been using a similar one: http://regex.powertoy.org/ http://regex.powertoy.org/ The latter supports several languages' regex dialects, and I like the visual way it displays group matches, particularly when groups are nested. It can be a bit clunky, though, whereas Rubular is pretty clean and usable.

iamwil 17y ago

I didn't see it mentioned, but, btw, this code allows a method to introspect to figure out what the method name that's currently being executed. caller[0][/`([^']*)'/, 1] Note that you only need to do this for Ruby 1.8. In Ruby 1.9, there will be a __method__() and __callee__() method that does the same thing.

grandalf 17y ago

(foo){2,5}