Regex: how to match overlapping patterns (maybe Python specific)

Question

I have a string that looks like this: "XaXbXcX". I'm looking to match any lowercase letters surrounded by X on either side. I tried this in Python, but I'm not getting what I'm looking for:

import re
str = "XaXbXcX"
pattern = r'X([a-z])X'
matches = re.findall(pattern, str) # gives me ['a', 'c']. What about b?

Answer 1

You can use a lookbehind assertion:

pattern = r'(?<=X)([a-z])X'