regex findall overlapped does not give match if one of them is a prefix of the other

Question

import regex

product_detail = "yyy target1 target2 xxx".lower()
p1 = r"btarget1b|btarget1 target2b"
p2 = r"btarget2b|btarget1 target2b"
for pattern in [p1, p2]:
    matches = regex.findall(pattern, product_detail, overlapped=True)
    print(matches)

why does matches from p1 only give ['target1'] as output, without 'target1 target2'

but matches from p2 can successfully give ['target1 target2', 'target2'] as output.

Also if you can provide a fix, how do i generalise it?
i have a list of 10000 target words and its not going to be feasible to hardcode them.

Asked By: leonardltk1

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Source

Answer 1

Here is an example of what I had in mind with my comment on building a list of patterns separating common prefixes:

import regex  # I'm actually using re (don't have regex)

product_detail = "yyy target1 target2 xxx".lower()

keywords = ["target1","target2","target1 target2","target3"]

from itertools import accumulate, groupby, zip_longest

keywords.sort()
groups   = accumulate(keywords,lambda g,k:g if k.startswith(g) else k)
patterns = ( g for _,(*g,) in groupby(keywords,lambda _:next(groups)) )
patterns = ( filter(None,g) for g in zip_longest(*patterns) )   
patterns = [r"b" + r"b|b".join(g) + r"b" for g in patterns]

# [r'btarget1b|btarget2b|btarget3b', r'btarget1 target2b']

for pattern in patterns:
    matches = regex.findall(pattern, product_detail)
    print(matches)

output:

['target1', 'target2']
['target1 target2']

Answered By: Alain T.

regex findall overlapped does not give match if one of them is a prefix of the other

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