Hacker News Reader

Comment by Maro | Hacker News Reader

You might like:

So you can write:

  username = rxe.one_or_more(rxe.set([rxe.alphanumeric(), '.', '%', '+', '-']))
  domain = rxe.one_or_more(rxe.set([rxe.alphanumeric(), '.', '-']))
  tld = rxe.at_least_at_most(2, 6, rxe.set([rxe.range('a', 'z'), rxe.range('A', 'Z')]))
  email = (rxe
    .exactly(username)
    .literal('@')
    .exactly(domain)
    .literal('.')
    .exactly(tld)
  )

View on HN

This seems cool, but I think that's mostly because the regex you think of as a point of comparison is something like

    r'^[\w.%+-]+@[\w.-]+\.[a-zA-Z]{2,6}$'

which does look awful. But there's no reason you can't do

    username = r'[\w.%+-]+'
    domain = r'[\w.-]+'
    tld = r'[a-zA-Z]{2,6}'
    email = username + r'@' + domain + r'\.' + tld

which is arguably easier to read than the rxe version for someone familiar with regex.

wow I didn't know you could concatenate regexes, thanks

Why not? They're just strings until they're compiled. "Code is data"

The thought of doing this literally didn’t occur to me... I think this is great!

Well I suppose the r in front of them in python made them look just enough "not a normal string" for me to forget how the + operator might act.

My day-to-day experience is in nodejs, where adding one regex object to another coerces them to normal strings first

[edit: hey neat, the hackernews form strips emoji from comments, I wonder if that's just ranges of unicode or if there's some crazy regex going on :D]

In Javascript you just need to wrap in `new RegExp(r1 + r2 + r3)`.

Yes, an rxe is longer. But: I've been using regexps was 20 years and I can't remember them (both reading and writing). My brain swaps it out, partly bc I know it's one SO away. But that's bad for code readability.

And/or use verbose mode -- re.VERBOSE or (?x) --for comments and whitespace.

I actually find these too verbose. May be because I didn't know about them when I started out, was using regex in cli tools and Perl scripts.

There's also a module [1] which already has collection of common regex to match dates, links, emails, etc.

[1] https://github.com/madisonmay/CommonRegex

I use the below to extract email addresses. Took from some website some time ago and made super light changes to it. Not sure if this is the best but it has served me fairly well.

email_reg = re.compile (r'''

([a-zA-Z0-9._%+-]+ #First name and last name

@ #@ sign

[a-zA-Z0-9._%+-]+ #domain name

\.[a-zA-Z]{2,10}) #.com

''',re.VERBOSE)

I would not allow the % sign.

You should allow “$” on the left; as per the RFC...

Why I hate regex :) . You think you know it but, you never really do.

That's about the email RFC, not about regex syntax.

Ok cool.

To me "exactly" means the same as "literal". (I understand here its a full pattern match)

Never heard about the rxe but it looks like something I could use - thanks.

I'll have to look into this. In some limited cases verbosity that leads to a more obvious and understandable presentation is preferable, at least to me.

Too verbose, I prefer good old regular expression.

Completely agree. If you know good old regular expressions, then this rxe definition is actually harder to read. This is how APL programmers must feel when they look at code in popular programming languages.

This is excellent, I prefer this.

10 lines to replace maybe 20 characters. How horribly verbose.

But that is exactly what I like about it. I rarely have to use regex, but when I do have to write or change something I always have to spend 15 mins reading (remembering) most of the things about it again, this would help me understand my old code way better.

This is good point, and without trying to debate anything, regex is something of an art form for some people and I guess as many people are averse to it as there are high school people hating Shakespear.

But to give a bit of substance, you can often use a dictionary type approach in a situation where regex is needed. Example: replacing accented latin with normal (ascii) latin.

I do sometimes pride myself in necromancing skills of resurrection old Perl scripts from perlmonks.com but I suspect it is more of a hobby that out of absolute necessity. I find the memes about Perl/Python and Starwars to be pretty funny and much more entertaining than people actually debating programming languages. [1]

[1] https://www.python.org/doc/humor/#python-vs-perl-according-t...

That describes all of Python, to an APL programmer.

Reply on news.ycombinator.com