How to implement "positional-only parameter" in a user defined function in python?

Question

How can I implement "positional-only parameter" for a function that is user defined in python?

def fun(a, b, /):
    print(a**b)

fun(5,2)        # 25
fun(a=5, b=2)   # should show error

Answer 1

Update: this answer will become increasingly out-dated; please see Eugene Yarmash's answer instead.

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The only solution would be to use a *-parameter, like so:

def fun(*args):
    print(args[0] ** args[1])

But this comes with its own problems: you can't guaranteed the caller will provide exactly two arguments; your function has to be prepared to handle 0 or 1 arguments. (It's easy enough to ignore extra arguments, so I won't belabor the point.)