Python regex to match multiple unique values

Question

I need to match a string with specific letters but none of the letters should be duplicated. For example, [AEIOU] should not match 'AAEIOU' or 'AAEEIOU'. It should only match 'AEIOU' and the order of the letters should not matter. I tried using the exact quantifier with {} but did not work.

So you want to check if any string has duplicate letters ex ('aaxds' - true, 'hdks' - false, 'kshk' - true)? Or only if the duplicate it right next to the same character? Or is it only the one string 'AEIOU' — Garret
– Garret, Commented Mar 22, 2018 at 3:01
You might not need regex for this.... You could filter on something like all(s.count(char) == 1 for char in 'AEIOU') probably a simpler solution than that. Can you provide some expected inputs and outputs? — sytech
– sytech, Commented Mar 22, 2018 at 3:01

user3483203 · Accepted Answer · 2018-03-22 03:01:45Z

2

You can use negative lookahead:

^(?!.*(.).*\1)[AEIOU]+$

Whatever you put in the brackets will be the subset of characters you select from.

>>> import re
>>> tests = ['AAEIOU', 'AAEEIOU', 'AEIOU']
>>> for test in tests:
..    print(re.match(r'^(?!.*(.).*\1)[AEIOU]+$', test))
None
None
<_sre.SRE_Match object; span=(0, 5), match='AEIOU'>

answered Mar 22, 2018 at 3:01

user3483203

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3 Comments

sytech Over a year ago

Good reference link with test cases. Excellent.

user3483203 Over a year ago

I have this regex saved for reference, pretty sure this is almost a duplicate. Just can't find the original.

Mauricio Cortazar Over a year ago

really good regex, can you explain it a little bit, I know what is lookaround but I didn't understand this one

William · Accepted Answer · 2018-03-22 03:01:34Z

0

This maybe inefficient, but maybe use counters? Construct a counter for each, then check if they are equal?

answered Mar 22, 2018 at 3:01

William

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Comments

sytech · Accepted Answer · 2018-03-22 03:12:02Z

0

Not using regex, but you can use python string methods to count characters in a string. This can be used to develop a filter function that, effectively, can get you the results you want.

def has_all_unique(s):
    """Returns True of the string has exactly 1 of each vowel"""
    return all(s.count(char) == 1 for char in 'AEIOU')

tests = ['AAEIOU', 'AAEEIOU', 'AEIOU']

for match in filter(has_all_unique, tests):
    print(match)

Result would be just the one match meeting the condition,

AEIOU

This isn't the most performant option, but is simple and readable.

answered Mar 22, 2018 at 3:12

sytech

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2 Comments

sytech Over a year ago

@MauricioCortazar appreciate your opinion, but I must disagree in this case. I love regex, it can be very expressive and take down deadly problems with a few characters... but put ^(?!.*(.).*\1)[AEIOU]+$ and all(s.count(char) == 1 for char in 'AEIOU') in front of 10 junior engineers and I think the results would speak to which one is easier to understand and describe without a reference or regex parser.

Mauricio Cortazar Over a year ago

you're right, but i assume that everyone know regex

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