Python development tools you can’t live without

I’m working on a series of columns for Python Magazine in which I
will be talking about development tools. The first “episode” appears in
the January 2008 issue and covers testing tools like frameworks and
runners. I have several more columns plotted out, but want to make sure
I cover the topics well and don’t miss out on mentioning a new or small
tool just because I haven’t heard about it myself.

So, I’m looking for feedback about the tools you just can’t (or don’t
want to) live without. Tell me all about your development environment,
editor, shell, debugger, IDE, version control system, etc. What
libraries (in addition to the standard library) do you use on a regular
basis? Is there any one thing that you would identify as being so
necessary for your Python work that if it was taken away you’d have to
give up and use another language? (And “the interpreter” is already on
the list, thanks.)

If you’re building a new development tool you think I should look at
for the series, post a link in a comment here or tag it with
pymagdifferent on and I’ll review it. I can’t promise
that everything will make it into the columns right away, but it will
eventually. Unusual or unique entries are more likely to be covered

It seems like everyone and their brother is building an editor, so if
that’s your game at least tell me why you think yours is
better/different from all the others. There are some problems with text
editing that are not easily solved, so if you have a killer feature make
sure you point that out. That goes double for templating languages –
highlight your special strengths.