Shell Sort implementation in Python

shell_sort.py

from math import ceil


def _return_list_gaps(size, ratio=None):
    gaps = list()
    if not ratio:
        ratio = 2.2
    while size > 1:
        size = ceil(size / ratio)
        gaps.append(size)
    return gaps
    

def shell_sort(array, decrescent=False, gaps=None, ratio=None):    
    if len(array) <= 1:
        return array

    # If no custom list of gaps was passed, defaults to the 2.2 ratio, and
    # builds a list of gaps to this ratio
    if not gaps:
        gaps = _return_list_gaps(len(array), ratio=ratio)
    # Guarantees that the list is in decrescent order
    gaps = sorted(gaps, reverse=True)

    for gap in gaps:
        for x in range(gap, len(array)):
            temp = array[x]
            y = x
            while y > 0 and ((decrescent and y >= gap and array[y - gap] < temp) or
                            (not decrescent and y >= gap and array[y - gap] > temp)):
                array[y] = array[y - gap]
                y = y - gap
            array[y] = temp
    return array