merge_sort implementation in python

merge_sort.py

def merge_sort(array):
    if len(array) == 1:
        return [array[0]]
    elif len(array) == 2:
        if array[0] > array[1]:
            return [array[1], array[0]]
        return [array[0], array[1]]
    mid = len(array) // 2
    left = merge_sort(array[0:mid])
    right = merge_sort(array[mid:])
    # merge
    out = []
    i, j = 0, 0
    while i < len(left) and j < len(right):
        if left[i] < right[j]:
            out.append(left[i])
            i += 1
        else:
            out.append(right[j])
            j += 1
    while i < len(left):
        out.append(left[i])
        i += 1
    while j < len(right):
        out.append(right[j])
        j += 1
    return out