CODEWITHSUNDEEP
pythonregexparsing
Deepak
Deepak

Reputation: 575

regex with optional block of text

I'm using regex to parse structured text as below, with caret symbol marking what I'm trying to match:

block 1
^^^^^^^
    subblock 1.1
        attrib a=a1
    subblock 1.2
        attrib b=b1
                 ^^
block 2
    subblock 2.1
        attrib a=a2
block 3
^^^^^^^
    subblock 3.1
        attrib a=a3
    subblock 3.2
        attrib b=b3
                 ^^

A subblock may or may not appear inside a block, e.g.: subblock 2.2.

The expected match is [(block1,b1), (block3,b3)].

/(capture block#)[\s\S]*?attrib\sb=(capture b#)/gm

But this ends up matching [(block1, b1), (block2, b3)].

Where am I doing the regex wrong?

Upvotes: 1

Views: 4278

Answers (2)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 627609

You can use

(?m)(^block\s*\d+).*(?:\n(?!block\s*\d).*)*\battrib\s*b=(\w+)

See the regex demo

The regex is based on an unroll the loop technique. Here is an explanation:

  • (?m) - multiline modifier to make ^ match the beginning of a line
  • (^block\s*\d+) - match and capture the block + optional whitespace(s) + 1+ digits (Group 1)
  • .* - matches the rest of the line (as no DOTALL option should be on)
  • (?:\n(?!block\s*\d).*)* - match any text after that is not a word block followed with optional whitespace(s) followed with a digit (this way, a boundary is set)
  • \battrib\s*b=(\w+) - match a whole word attrib followed with 0+ whitespaces, literal b=, and match and capture 1+ alphanumerics or underscore (note: this can be adjusted as per your real data) with (\w+)

Python demo:

import re
p = re.compile(r'(?m)(^block\s*\d+).*(?:\n(?!block\s*\d).*)*\battrib\s*b=(\w+)')
s = "block 1\n    subblock 1.1\n        attrib a=a1\n    subblock 1.2\n        attrib b=b1\nblock 2\n    subblock 2.1\n        attrib a=a2\nblock 3\n    subblock 3.1\n        attrib a=a3\n    subblock 3.2\n        attrib b=b3"
print(p.findall(s))

Upvotes: 2

Byte Commander
Byte Commander

Reputation: 6776

What about this regex? https://regex101.com/r/yZ4fL9/1

block (\d).*?attrib b=b(\1)

Upvotes: 0

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