python regex return result without characters used for matching

Question

i would like to perform regex matching, but exclude from the result the characters used for the matching. consider this sample code

import re
string="15  83(B): D17"
result=re.findall(r'\(.+\)',string)
print(result)

here's what i get: ['(B)']

here's what i'd like to have: ['B']

i'm after a generic solution to exclude pattern characters used to start/end a match from the result, not just a solution for this precise case. for example instead of just ( and ) i could have used more complex patterns to start/end matching, and i still would not want to see them as part of the result.

anubhava · Accepted Answer · 2017-01-13 18:58:23Z

2

You need to use a capturing group for the text you need in output like this:

>>> string="15  83(B): D17"
>>> print re.findall(r'\((.*?)\)', string)
['B']

(.*?) is capturing group to match and capture 0 or more characters, non-greedy

In general you can replace starting ( and ending ) with anything you have as before and after your match.

answered Jan 13, 2017 at 18:58

anubhava

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2 Comments

freeaks Over a year ago

thanks for the reply, it works for this example, but if i wanted to replace '(' with '8' and ')' with '1' to get anything between so: '3(B): D', then it doesn't work? i'm not much skilled with regex as you can see. i would like a start pattern and ending pattern and get everything between, excluding both start /end delimiters. is that not appropriate for regex ?

anubhava Over a year ago

Use print re.findall(r'8(.*?)1', string) and you will get ['3(B): D']

Eduardo Lynch Araya · Accepted Answer · 2017-01-13 19:17:25Z

0

The correct regex is it

r"(?<=\()(.*)(?=\))"

U can change ( and ) for anything

answered Jan 13, 2017 at 19:17

Eduardo Lynch Araya

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Comments

glibdud · Accepted Answer · 2017-01-13 19:17:54Z

0

Lookaheads and lookbehinds can be used to assert that characters are present before and after a certain position without including them in a match.

>>> string = "15  83(B): D17"
>>> re.findall(r'(?<=\().+(?=\))', string)
['B']

Here, (?<=\() is a positive lookbehind that asserts that an open parenthesis character comes immediately before this position. (?=\)) is a positive lookahead that asserts that a close parenthesis character comes immediately after.

Search the re module documentation for the terms "lookahead" and "lookbehind" for more information.

answered Jan 13, 2017 at 19:17

glibdud

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