如何找到数组拐点的估计值？(Python)

def calculate_slope(arr):
    slopes = []
    for i in range(1, len(arr)):
        diff = arr[i] - arr[i-1]
        if diff > 0:
            slopes.append(1)
        elif diff < 0:
            slopes.append(-1)
        else:
            slopes.append(0)
    return slopes

def find_inflection_point(arr):
    slopes = calculate_slope(arr)
    inflection_points = []
    for i in range(1, len(slopes)):
        if slopes[i] != slopes[i-1]:
            inflection_points.append(i)
    return inflection_points

arr = [1, 2, 3, 4, 5, 4, 3, 2, 1]
inflection_points = find_inflection_point(arr)
estimated_value = sum(arr[inflection_points[0]:inflection_points[1]+1]) / len(arr[inflection_points[0]:inflection_points[1]+1])
print("估计值为:", estimated_value)