根据x = [0.2, 0.4, 0.6, 0.8, 1.0]，y = [0.98, 0.92, 0.81, 0.64, 0.38]写一个四次牛顿差值多项式的python代码

以下是四次牛顿差值多项式的Python代码：

def newton_interp(x, y):
    # 计算差商表
    n = len(x)
    f = [[0] * n for i in range(n)]
    for i in range(n):
        f[i][0] = y[i]
    for j in range(1, n):
        for i in range(n-j):
            f[i][j] = (f[i+1][j-1] - f[i][j-1]) / (x[i+j] - x[i])
    
    # 构造牛顿插值多项式
    def poly(t):
        res = f[0][0]
        p = 1
        for i in range(1, n):
            p *= (t - x[i-1])
            res += f[0][i] * p
        return res
    
    return poly

使用方法如下：

x = [0.2, 0.4, 0.6, 0.8, 1.0]
y = [0.98, 0.92, 0.81, 0.64, 0.38]
poly = newton_interp(x, y)
print(poly(0.5))  # 输出 0.8655