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')

Answer 2

re.sub('([a-z])([A-Z])', '\\1 \\2', 'TheFileName.txt')

EDIT: StackOverflow eats some \s, when not in 'code mode'... Because I forgot to add a newline after the code above, it was not interpreted in 'code mode' :-((. Since I added that text here I didn't have to change anything and it's correct now.

Answer 3

Another possible regular expression using a look behind:

(?<!^)([A-Z])

Answer 4

It is not clear what you want to do if the filename is Hello123There.txt. So, if you want a space before all capital letters regardless of what precedes them, you can:

import re

def add_space_before_caps(text):
    "Add a space before all caps except at start of text"
    return re.sub(r"(?<!^)(?=[A-Z])", " ", text)

>>> add_space_before_caps("Hello123ThereIBM.txt")
'Hello123 There I B M.txt'