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Lucretius
Lucretius

Reputation: 3

Regex for matching only capitalized words stuck together (i.e. not separated by whitespace)

I have a long list of strings which are all random words, all of them capitalized, such as 'Pomegranate' and 'Yellow Banana'. However, some of them are stuck together, like so: 'AppleOrange'. There are no special characters or digits.

What I need is a regular expression on Python that matches 'Apple' and 'Orange' separately, but not 'Pomegranate' or 'Yellow'.

As expected, I'm very new to this, and I've only managed to write r"(?<!\s)([A-Z][a-z]*)"... But that still matches 'Yellow' and 'Pomegranate' . How do I do this?

Upvotes: 0

Views: 113

Answers (2)

The fourth bird
The fourth bird

Reputation: 163362

If they all start with an uppercase char and optional lowercase chars, you can make use of lookarounds and an alternation to match both variations

(?<=[a-z])[A-Z][a-z]*|[A-Z][a-z]*(?=[A-Z])

The pattern matches:

  • (?<=[a-z]) Assert a-z to the left
  • [A-Z][a-z]* match A-Z and optional chars a-z
  • | or
  • [A-Z][a-z]* match A-Z and optional chars a-z
  • (?=[A-Z]) Assert A-Z to the right

Regex demo

Example

import re

pattern = r"(?<=[a-z])[A-Z][a-z]*|[A-Z][a-z]*(?=[A-Z])"
s = ("AppleOrange\nPomegranate Yellow Banana")

print(re.findall(pattern, s))

Output

['Apple', 'Orange']

Another option could be getting out of the way what you don't want by matching it, and use a capture group for what you want to keep and remove the empty entries from the result:

(?<!\S)[A-Z][a-z]*(?!\S)|([A-Z][a-z]*)

Regex demo | Python demo

import re

pattern = r"(?<!\S)[A-Z][a-z]*(?!\S)|([A-Z][a-z]*)"
s = ("AppleOrange\nPomegranate Yellow Banana")

print([x for x in re.findall(pattern, s) if x])

Upvotes: 1

Nestor Silva
Nestor Silva

Reputation: 101

This work:

import re
from collections import deque

pattern = r'([A-Z]{2,}(?=[A-Z]|$)|[A-Z](?=[a-z]|$))'
chunks = deque(re.split(pattern, 'AppleOrange'))

result = []
while len(chunks):
  buf = chunks.popleft()
  if len(buf) == 0:
    continue
  if re.match(r'^[A-Z]$', buf) and len(chunks):
    buf += chunks.popleft()
  result.append(buf)

print(result)

Output:

['Apple', 'Orange']

Check the OP here

Upvotes: 1

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