I like Python and use it a lot, but Dhall has several guarantees that Python doesn't. If you hand someone clever a Python interpreter, they can and will find a way to run rm -rf / or what-have-you, no matter what safeguards you put in place. Dhall also guarantees that it will terminate, which is pretty useful if you're embedding it in something else. In Python you could pretty easily accidentally or purposefully get into a while True loop.