Python regex: Turn "ThisFileName.txt" into "This File Name.txt"

Question

I'm trying to add a space before every capital letter, except the first one.

Here's what I have so far, and the output I'm getting:

>>> tex = "ThisFileName.txt"
>>> re.sub('[A-Z].', ' ', tex)
' his ile ame.txt'

I want: 'This File Name.txt'

(It'd be nice if I could also get rid of .txt, but I can do that in a separate operation.)

Answer 1

Key concept here is backreferences in regular expressions:

import re
text = "ThisFileName.txt"
print re.sub('([a-z])([A-Z])', r'\1 \2', text)
# Prints: "This File Name.txt"

For pulling off the '.txt' in a reliable way, I recommend os.path.splitext()

import os
filename = "ThisFileName.txt"
print os.path.splitext(filename)
# Prints: ('ThisFileName', '.txt')