Bubble sort recursive implementation in Python

bubble.py

def bubble(l_elems, is_sorted, step):
    if step is 1 or is_sorted:
        # base case: l_elems is already sorted or we pass through the list len(l_elems) times
        return l_elems
    else:
        is_swapped = False
        for i in range(len(l_elems) - 1):
            # compares each pair of adjacent items and swaps them if they are in the wrong order
            if l_elems[i] > l_elems[i + 1]:
                is_swapped = True
                l_elems[i], l_elems[i + 1] = l_elems[i + 1], l_elems[i]
        # if is_swapped is True, the algorithm needs to pass through the list again
        return bubble(l_elems, not is_swapped, step - 1)

print(bubble(range(10,0,-1), False, len(range(10,0,-1))))
print(bubble([5,6,5,3,3], False, len([5,6,5,3,3])))

Nice recursive implementation! I understand the code and it's not hard to follow. Comments are clear and helpful.
Running it in a console produces correct results for test cases, and as far as I can see any possible cases... I tried it with an empty array and it worked fine. My only suggestions are two very minor nits:

1. "l_elems" is kind of harder to read with the underscore, maybe just use "elems" ?
2. Maybe have two functions, a recursive inner function and an outer wrapper function that only takes an array, that way you don't have to supply "False" and the length of the array to the outer function, since those are defaults or can be determined from just the array.

@PaulMorris thanks for the comments they are very helpful!