TensorFlow has mappers/reducers for feature engineering, and it's Python - so you will inevitably do what you want in there. But yes, you have a point there. How do you debug this thing, though?
You have a good point about debugging. So far my approach has been to write quite long and explanatory error messages (like this https://github.com/uber/ludwig/blob/9c9e5de56dcad89461c5d2ec... for instance) and as detailed documentation as I can and, at least when people used it internally, that has been enough. But I'm definitely open to suggestions here.
