Pretty easy with modified merge sort.

def insertionSort(arr):
    arr, count = mergeCountInversions(arr)
    return count

def mergeCountInversions(arr):
    if len(arr) < 2:
        return arr, 0

    c = len(arr) // 2

    left, lc = mergeCountInversions(arr[:c])
    right, rc = mergeCountInversions(arr[c:])

    merged = [0] * len(arr)
    count = lc + rc

    lpos = 0
    rpos = 0

    for i in range(len(arr)):
        if lpos == len(left):
            side = 'r'
        elif rpos == len(right):
            side = 'l'
        elif left[lpos] <= right[rpos]:
            side = 'l'
        else:
            side = 'r'

        if side == 'l':
            merged[i] = left[lpos]
            lpos += 1
        else:
            merged[i] = right[rpos]
            rpos += 1
            count += len(left) - lpos

    return merged, count