How do I write a regex to replace a word but keep its case in Python?

Question

Is this even possible?

Basically, I want to turn these two calls to sub into a single call:

re.sub(r\'\\bAword\\b\', \'Bword\', mystring)
re.sub(r\'\         


        

Answer 1

You can pass a lambda function which uses the Match object as a parameter as the replacement function:

import re
re.sub(r'\baword\b', 
       lambda m: m.group(0)[0].lower() == m.group(0)[0] and 'bword' or 'Bword',
       'Aword aword', 
       flags=re.I)
# returns: 'Bword bword'