Preg_match_all with nested matches - regex

Question

i'm developing a template system and running into some issues.
The plan is to create HTML documents with [#tags] in them.
I could just use str_replace (i can loop trough all posible replacements), but i want to push this a little further ;-)
I want to allow nested tags, and allow parameters with each tag:
[#title|You are looking at article [#articlenumber] [#articlename]]
I would like to get the following results with preg_match_all:
[0] title|You are looking at article [#articlenumber] [#articlename]
[1] articlenumber
[2] articlename
My script will split the | for parameters.
The output from my script will be something like:
<div class='myTitle'>You are looking at article 001 MyProduct</div>
The problem i'm having is that i'm not exprerienced with regex. Al my paterns results almost what i want, but have problems with the nested params.
\[#(.*?)\]
Will stop at the ] from articlenumber.
\[#(.*?)(((?R)|.)*?)\]
Is more like it, but it doesn't catch the articlenumber; https://regex101.com/r/UvH7zi/1
Hope someone can help me out! Thanks in advance!

Answer 1

You cannot do this using general Python regular expressions. You are looking for a feature similar to "balancing groups" available in the .NET RegEx's engine that allows nested matches.
Take a look at PyParsing that allows nested expression:
from pyparsing import nestedExpr
import pyparsing as pp
text = '{They {mean to {win}} Wimbledon}'
print(pp.nestedExpr(opener='{', closer='}').parseString(text))
The output is:
[['They', ['mean', 'to', ['win']], 'Wimbledon']]
Unfortunately, this does not work very well with your example. You need a better grammar, I think.
You can experiment with a QuotedString definition, but still.
import pyparsing as pp
single_value = pp.QuotedString(quoteChar="'", endQuoteChar="'")
parser = pp.nestedExpr(opener="[", closer="]",
content=single_value,
ignoreExpr=None)
example = "['#title|You are looking at article' ['#articlenumber'] ['#articlename']]"
print(parser.parseString(example, parseAll=True))

Answer 2

I'm typing this on my phone so there might be some mistakes, but what you want can be quite easily achieved by incorporating a lookahead into your expression:
(?=\\[(#(?:\\[(?1)\\]|.)*)\\])
Edit: Yup, it works, here you go: https://regex101.com/r/UvH7zi/4
Because (?=) consumes no characters, the pattern looks for and captures the contents of all "[#*]" substrings in the subject, recursively checking that the contents themselves contain balanced groups, if any.

Answer 3

here is my code:
#\w+\|[\w\s]+\[#(\w+)]\s+\[#(\w+)]
https://regex101.com/r/UvH7zi/3

Answer 4

For now i've crated a parser:
- get all opening tags, and put their strpos in array
- loop trough all start positions of the opening tags
- Look for the next closingtag, is it before the next open-tag? than the tag is complete
- If the closingtag was after an opening tag, skip that one and look for the next (and keep checking for openingtags in between)
That way i could find all complete tags and replace them.
But that took about 50 lines of code and multiple loops, so one preg_match would be greater ;-)