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?

>Solution :

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']