Why Final params are not allowed?

[Rudxain]

python/peps#3102

[sobolevn]

Why was that decision taken? What's the rationale?
I haven't read 100% of that PEP, but I'm pretty sure my question isn't answered anywhere.
I would really love to mark params as immutable! And this would make Py more suitable for purely-functional-programming

Final does not make objects immutable. It makes names un-reassignable. It might theoretically work like this:

def some(a: Final[list[int]]):
   a.append(1)  # will still be ok
   a = []  # not ok, but why?

In my opinion, this was never implemented because this is not needed (prove me wrong by providing actual use-cases).
It is a common practice to reassign function params in a function body in Python.
And there's nothing wrong with that :)

[Rudxain]

I suppose you think Final is only useful in the global scope, because mutable global vars are bad practice in every language (specially if these are implicitly exported).

Idiomatic Python is (mostly) about being concise, so it makes sense to use Final sparingly.

I personally prefer to use Final everywhere possible, except when a var is in a narrow scope (short lifetime).

Functions can get big, so Final may be very useful in those cases. Of course, big fns should be split into modular fns, to prevent unmaintainable code from growing