file1.txt
file2.txt
file3
file4.
.file5
file6.txt
file7
file8.txt

I came up with (?m)^[^.\n]+\.?$. If you want to include .file5 with the "no extension" files, then (?m)^\.?[^.\n]+\.?$. ((?m) is the multiline flag which causes ^$ to match beginning/end of lines in addition to the normal beginning/end of the whole string.)

Interactively:

from imisc import match
list = 'file1.txt\nfile2.txt\nfile3\nfile4.\n.file5\nfile6.txt\nfile7\nfile8.txt'
match('(?m)^\.?[^.\n]+\.?$', list)

With results:

a match!
1) start: 20, end: 25, str: file3
2) start: 26, end: 32, str: file4.
3) start: 33, end: 39, str: .file5
4) start: 50, end: 55, str: file7
global replace (_._):
file1.txt
file2.txt
_._
_._
_._
file6.txt
_._
file8.txt

It's not Qt, but it's what I know. :-)

I experimented with your variation and it works well for getting the None result. In my case, I was reassembling base + 'new string' + ext, so it was more appropriate to have the ext be an empty string instead of None, but of course other cases would be nicer with None.

And! In the end I went with the simpler Python method anyway:

base, ext = os.path.splitext(filename)
new_filename = base + '.descripted' + ext

(Where they also decided to go with the empty string result when there is no extension.)

:-)

Thanks again for visiting!

I really appreciated your article. It saved me a lot of time not having to find it out by myself. You do point out a very elegant but simple solution!

Matching filenames with regex is useful to validate filenames that are expected to satisfy rules expressed as patterns stored somewhere else.

However, I would suggest a minor change in your expression:
(.+?)(?:\.([^.]*$)|$) or (.+?)(?:(\.[^.]*$)|$). It creates a group that contains the extension or None if there is no extension (respectively, without or with the point of the extension). Personally, I prefer getting None if an optional element is not present in the matched string.

Also, it might be useful matching the directory assuming a path to a file instead of a filename. By following your advice, I was easy to find out another regex pattern: ^(.*/)?(?:$|(.+?)(?:(\.[^.]*$)|$))

Best regards, Daniel

I just wanted to point out Thunar's Bulk Rename extension (install using apt-get install thunar). In this forum thread over at the Ubuntu Forums I explain how to use nautilus-actions to be able to use it from the context menu within Nautilus.

See this screenshot for a look at Bulk Rename.

*drool* I love GUIs...