I'm not used to REPL-Driven development, but I took a course on a image-based language, Pharo, that follows the tradition of instant feedback and deep introspection from Smalltalk IDEs, said to share many properties with REPLs. At work I do my programming mostly in Python, and always miss the things enabled by the Pharo environment. I wonder if it's possible, and how hard it would be, to build a similar image-based workflow around Python. At least it seems some people managed to do that for TCL. See http://www.xdobry.de/tclsqueak/