Regex findall start() and end() ? Python

Question

i'm trying to get the start and end positions of a query in sequence by using re.findall

import re

sequence = 'aaabbbaaacccdddeeefff'

query = 'aaa'

findall = re.findall(query,sequence)

>>> ['aaa','aaa']

how do i get something like findall.start() or findall.end() ?

i would like to get

start = [0,6]
end = [2,8]

i know that

search = re.search(query,sequence)

print search.start(),search.end()

>>> 0,2

would give me only the first instance

Ashwini Chaudhary · Accepted Answer · 2013-07-11T22:25:56.797

24

Use re.finditer:

>>> import re
>>> sequence = 'aaabbbaaacccdddeeefff'
>>> query = 'aaa'
>>> r = re.compile(query)
>>> [[m.start(),m.end()] for m in r.finditer(sequence)]
[[0, 3], [6, 9]]

From the docs:

Return an iterator yielding MatchObject instances over all non-overlapping matches for the RE pattern in string. The string is scanned left-to-right, and matches are returned in the order found.

edited Jul 11 '13 at 22:25

answered Jul 11 '13 at 22:20

Ashwini Chaudhary

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Instead of `[m.start(), m.end()]` you can also just use `m.span()` which returns a tuple of the start and end indicies. – Michael Hall Jun 23 '17 at 06:03
your code fails for -> sequence = 'aaadaa' query = 'aa' , Yours output (0, 2) (4, 6) , Correct output (0, 1) (1, 2) (4, 5) – Sanjit Prasad Jun 16 '18 at 14:23
@SanjitPrasad It says clearly in the quoted text: "all non-overlapping matches..." – Ashwini Chaudhary Jun 16 '18 at 20:54
ooh sorry for that, what if we need to find overlapping matches too. – Sanjit Prasad Jun 17 '18 at 07:13

score 4 · Answer 2 · answered Jul 11 '13 at 22:21

You can't. findall is a convenience function that, as the docs say, returns "a list of strings". If you want a list of MatchObjects, you can't use findall.

However, you can use finditer. If you're just iterating over the matches for match in re.findall(…):, you can use for match in re.finditer(…) the same way—except you get MatchObject values instead of strings. If you actually need a list, just use matches = list(re.finditer(…)).

score 2 · Answer 3 · answered Jul 11 '13 at 22:21

2

Use finditer instead of findall. This gives you back an iterator yielding MatchObject instances and you can get start/end from the MatchObject.

answered Jul 11 '13 at 22:21

tuckermi

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Regex findall start() and end() ? Python

3 Answers3