Often I use Python for exploratory purposes. Like, I got a bunch of data, and I want to know if a particular algorithm might work or not. I implement the algorithm, but realize the results don’t look good enough. So I tweak the algorithm, maybe even do major refactoring. Or maybe I realize my visualizations or metrics don’t capture what I need to see. Or maybe I must settle for some compromise?
I iterate on this repeatedly until I find something I’m happy about (or until I give up). Sometimes I end up with something completely different from my initial idea.
TDD won’t help me much here because the end result is unknown. For each iteration of this idea process I might even need to rewrite all the tests because none of them are valid anymore.