Merge Sort In Python

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def merge_sort(arr):
    if len(arr) <= 1:
        return

    mid = len(arr)//2

    left = arr[:mid]
    right = arr[mid:]

    merge_sort(left)
    merge_sort(right)

    merge_two_sorted_lists(left, right, arr)

def merge_two_sorted_lists(a,b,arr):
    len_a = len(a)
    len_b = len(b)

    i = j = k = 0

    while i < len_a and j < len_b:
        if a[i] <= b[j]:
            arr[k] = a[i]
            i+=1
        else:
            arr[k] = b[j]
            j+=1
        k+=1

    while i < len_a:
        arr[k] = a[i]
        i+=1
        k+=1

    while j < len_b:
        arr[k] = b[j]
        j+=1
        k+=1

if __name__ == '__main__':
    test_cases = [
        [10, 3, 15, 7, 8, 23, 98, 29],
        [],
        [3],
        [9,8,7,2],
        [1,2,3,4,5]
    ]

    for arr in test_cases:
        merge_sort(arr)
        print(arr)

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