This is great. Alexis King actually stated that, had she known how popular “Parse, Don’t Validate” had been, she would have written it in a language more widely used than Haskell.
Haskell's strong, static, non-reflective type system tends to make "parse, don't validate" produce code that also looks nicer. Which is great. So great that it steals a bit of the main message's valor.
In Python, though, it's really easy to just let your data be a dynamically typed list of dicts forever. So easy that parsing into something more strongly typed looks like a whole lot of extra effort. Upon looking at that sort of thing many a working Python programmer, myself included, hears the voice of GvR murmuring disparaging things about "academic" programmers down in the pit of their brain.
Which creates an opportunity to demonstrate all the ways the (arguably) more Pythonic way is actually a royal PITA when you try to make your code robust. Handling and reporting data validity errors gets scattered all over the code, which makes it annoying to maintain. Unit test suites get bloated because it's not obvious what inputs a function should be able to handle. Comments and docstrings to help keep track of this stuff begin to proliferate.
You otherwise get accustomed to some wishy-washy blobs of data that get passed around and find it normal. Maybe you include some ad hoc guard rails here and there, which catches the egregious errors, but there is always some lingering uncertainty. Some string that should have been an int, missing key here, the object which never had the validation check, etc
It is like unit-testing - more-up front work, but I could never go back to a world where I did not get these automated assurances. Sadly, I am a grug-brain which could only feel the lesson from personal experience.
there’s all the code correctness stuff that we all love. But the biggest benefit is making it so much easier to maintain other parts of the stack.
Following a stack trace into somebody else’s functions and you see that the args are completely untyped or just a bunch of ‘dict[str, Any]’ is the worst. But if you see those inputs as more narrowly typed data classes it makes it so much easier to grok what the function is supposed to do
Previously I had been somewhat sympathetic to Rich Hickey’s impassioned monologues about making maps first-class and how everything gets easier when you let data just be itself. But when I had to learn my way around code that someone else had written according to that philosophy… hoo boy. Clojure quickly got demoted from being one of my favorite languages to merely being one of my favorite write-only languages.