My personal choices are IPython and Jupyter, depending on whether I'm making plots. If you choose Jupyter, though, I caution that you should be careful you don't switch entirely away from modules and test suites. Jupyter can be too easy in a way.

This sounds quite a bit different from the sort of development work I do.

I can see how a REPL would be really useful when working with data, but for building out a webserver or desktop application, it doesn't have nearly as much value.

And tests have less value, or at least are more difficult to write, when you're not sure if an outlier is valuable information or junk to be discarded.