Question

this might be a rookie question, but how would you efficiently apply regex expressions on strings to retrieve parts of the string ? I have a concrete parsing to solve as an example.

If I have the string :

STRING[(val1)-{val2}-!val3!]

or

STRING[{val2}-!val3!-(val1)]

or

STRING[!val3!-(val1)-{val2}]

etc… (All 8 permutations of !val3!,(val2),{val1} that I won’t bother you with).

I can do several easy finds and splits on that to achieve my purpose, but how would you do things in a clean and safe way to get something like :

val1,val2,val3 = ... ?

UPDATE : in the string to parse, val1, val2 and val3 are variable inputs, and the three delimiters !! () {} are there to help me know where are the three values that each have another semantic meaning.

Answer 1

You can use lookahead assertions with capturing groups to find matches in any order:

import re
def matchany(subject):
    match = re.match(
        r"""
        (?=.*\(([^()]*)\))   # Find match between () --> group 1
        (?=.*\{([^{}]*)\})   # Find match between {} --> group 2
        (?=.*!([^!]*)!)      # Find match between !! --> group 3""", 
        subject, re.VERBOSE)
    return match.groups() if match else None

Then you can do

>>> matchany("STRING[(val1)-{val2}-!val3!]")
('val1', 'val2', 'val3')
>>> matchany("STRING[!val3!-(val1)-{val2}]")
('val1', 'val2', 'val3')
>>> matchany("STRING[(val1)-{val2}-!val3]")
>>>