How does the Python range function have a default parameter before the actual one?

So I'm writing a function that takes an optional list and extends it to the length specified. Rather than writing it as foo(n, list=None) I was wondering how I might emulate the behavior of Python's range function which works like:

>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(5, 10)
[5, 6, 7, 8, 9]

That is, with the default parameter first. For reference trying to naively set this up returns a syntax error:

def foo(x=10, y):
    return x + y
SyntaxError: non-default argument follows default argument

So I'm wondering, is this hard-coded into range? Or can this behavior be emulated?