I use the freeware editor ConText (for Windows only I'm afraid) from http://www.contexteditor.org/.
It includes language highlighters for a lot of languages including python. It also allows customisation to execute a command using the loaded files (e.g. execute the loaded python script) then capture the output and decode the line numbers where the problem occurred. -- Dave Moor
I use this too (it is VERY good). But now I also use SciTe as it is cross platform and allows you to run your scripts and see the output within the text editor (very cool). -- Peter Lucas