If you regard 'They're' as two words and don't need to find numbers, just use [a-zA-Z]+\b is enough.

Well, the way to distinguish ' from \b that I think up is to write re like this: [a-zA-Z]+('[a-zA-Z]+|\b)

The order is very important, if you write [a-zA-Z] after | , it will be ignore.

What's more, in python use ' in a string \' is necessary.

re.findall(r'[a-zA-Z]+(\'[a-zA-Z]+|\b)',string) 

##Warning##

There are some mistake use this re in Python. It works well in Sublime. I will try to fix it in several days. Thank you!