I've just uploaded my second Python Cookbook recipe. It's unfortunately not rocket science but it's application is potentially very useful. With this little function you can generate the next number in a string that contains at least one number.
The mini unittest is quite interesting perhaps:
$ python increment_strings.py from 10dsc_0010.jpg to 10dsc_0011.jpg from dsc_9.jpg to dsc_10.jpg from 0000001.exe to 0000002.exe from ref-04851 to ref-04852