Avoid consuming input in Regex

Asked Dec 31 '16 at 08:54

Active Dec 31 '16 at 09:03

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In Regex, I am given a string "abbabbabba" and I have to identify all the sub-strings having the pattern "abba" and when I try it this way:

import re
a=re.findall(r'abba','abbabbabba')
print(a)

I get my out put to be

['abba', 'abba']

Looking at the given string, there are 3 sub-strings of 'abba' but only two have been printed. This clearly means that the second sub-string which has its 'a' already consumed in 1st sub-string isn't allowing the function to identify the 2nd sub-string and hence it is directly jumping to the 3rd sub-string and hence only 2 'abba' sub-strings are printed. How to make sure that the input isn't consumed in this way and we get the output accordingly as:

['abba', 'abba', 'abba']

edited Dec 31 '16 at 09:03

Mohammad Yusuf

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asked Dec 31 '16 at 08:54

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`a=re.findall(r'(?=(abba))','abbabbabba')` – Wiktor Stribiżew Dec 31 '16 at 09:12
thanks @WiktorStribiżew :) since you have marked this as duplicate, I shall delete this question once you have acknowledged that I have understood this. – Dec 31 '16 at 09:31
Capturing inside a positive lookahead is a usual way to get overlapping matches. – Wiktor Stribiżew Dec 31 '16 at 09:38
@Anurag Don't delete it. If someone queries the title just like you have asked, he will find it easy to get to the original question. – Mohammad Yusuf Dec 31 '16 at 10:02

Avoid consuming input in Regex

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