How to match part of a string multiple overlapping times with regex

Question

I need a Python regex matching the part of a string multiple times:

My String: aa-bbb-c-dd

I would like to have groups like this:

aa-bbb
bbb-c
c-dd

Does somebody have an idea on how to do this?

Asked By: user1383029

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Source

Answer 1

You can use lookahead to get overlapping matches:

(?=b([A-Za-z]+-[A-Za-z]+)b)

See the regex demo.

Details:

(?= – start of a positive lookahead that matches a location that is immediately followed with
- b – a word boundary
- ([A-Za-z]+-[A-Za-z]+) – Group 1: one or more ASCII letters, -, one or more ASCII letters
- b – a word boundary
) – end of the lookahead.

In Python, use it with re.findall:

import re
text = "aaaa-bb-ccc-dd"
print( re.findall(r'(?=b([A-Z]+-[A-Z]+)b)', text, re.I) )
# => ['aaaa-bb', 'bb-ccc', 'ccc-dd']

See the Python demo. Note I changed [A-Za-z] to [A-Z] in the code since I made the regex matching case insensitive with the help of the re.I option. Make sure you are using the r string literal prefix or b will be treated as a BACKSPACE char, x08, and not a word boundary.

Variations

(?=b([^Wd_]+-[^Wd_]+)b) – matching any Unicode letters
(?=(?<![^Wd_])([^Wd_]+-[^Wd_]+)(?![^Wd_])) – matching any Unicode letters and the boundaries are any non-letters

Answered By: Wiktor Stribiżew

How to match part of a string multiple overlapping times with regex

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