I'd say it's not a good choice if like your example, you want to integrate with a mature web framework, or something else that only Python has (though Julia FFI

I'd say it's not a good choice if like your example, you want to integrate with a mature web framework, or something else that only Python has (though Julia FFI allows to call Python almost like you're writing python directly in the Julia code), or if you already have an infrastructure in Python. For run-of-the-mill numerical computation, like you said it's good writing loops and code that is really natural and run it fast. Most commonly used algorithms for data science and scientific computing are already written in Julia, you don't need to write them from scratch. But it's good to have libraries that you can easily inspect, understand and extend within your code.