Python：TypeError：'float'对象没有'__getitem__'属性

Question

我正在尝试在Python中实现粒子滤波算法，但遇到了这个错误：

x_P_update[i] = 0.5*x_P[i] + 25*x_P[i]/(1 + x_P[i]**2) + 8*math.cos(1.2*(t-1)) +     math.sqrt(x_N)*np.random.randn()
TypeError: 'float' object has no attribute '__getitem__'

我的代码：

import math
import numpy as np
import matplotlib.pyplot as plt

x = 0.1 #initial value
x_N = 1 #process noise covariance in state update
x_R = 1 #noise covariance in measurement
T = 75 #number of iterations
N = 10 #number of particles

V = 2
x_P = [None]*(N)

for i in xrange(0, N):
    x_P[i] = x + math.sqrt(V)*np.random.randn()

z_out = np.array([x**2 / 20 + math.sqrt(x_R) * np.random.randn()])  #the actual output vector for measurement values.
x_out = np.array([x])  #the actual output vector for measurement values.
x_est = np.array([x]); # time by time output of the particle filters estimate
x_est_out = np.array([x_est]) # the vector of particle filter estimates.

x_P_update = [None]*N
z_update = [None]*N
P_w = [None]*N

for t in xrange(1, T+1):
    x = 0.5*x + 25*x/(1 + x**2) + 8*math.cos(1.2*(t-1)) +  math.sqrt(x_N)*np.random.randn()
    z = x**2/20 + math.sqrt(x_R)*np.random.randn()
    for i in xrange(0, N):
        #each particle is updated with process eq
        x_P_update[i] = 0.5*x_P[i] + 25*x_P[i]/(1 + x_P[i]**2) + 8*math.cos(1.2*(t-1)) + math.sqrt(x_N)*np.random.randn()
        #observations are updated for each particle
        z_update[i] = x_P_update[i]**2/20
        #generate weights
        P_w[i] = (1/math.sqrt(2*math.pi*x_R)) * math.exp(-(z - z_update[i])**2/(2*x_R))

    P_w[:] = [ k / sum(P_w) for k in P_w]
#    print(np.where(np.cumsum(P_w, axis=0) >= np.random.rand()))

  #  print(index_tuple[0][1])
#    P_w_array = np.array(list(P_w))
#    indices = [i for i in range(len(P_w)) if np.cumsum(P_w_array) >= np.random.rand()]
    for i in xrange(0, N):
        index_tuple = np.where(np.random.rand() <= np.cumsum(P_w, axis=0))
        m = index_tuple[0][1]
        x_P = x_P_update[m]

    x_est = np.array([np.mean(x_P)])
    x_out = np.array([x_out, x])
    z_out = np.array([z_out, z])
    x_est_out = np.array([x_est_out, x_est])

我在这里使用了Matlab的代码，想学习如何用scipy在Python中实现这个算法。http://studentdavestutorials.weebly.com/particle-filter-with-matlab-code.html

我刚开始学习Python，遇到这个问题不知道怎么解决，麻烦大家帮帮我。

Answer 1

我不会逐个视频教程来帮你修正算法，但我可以告诉你为什么会出现这个错误。

在这一行：

x_P = x_P_update[m]

你把一个浮点数值赋给了一个数组，然后在外层循环中试图把它当作数组来访问。要解决这个错误，你需要更新它：

x_P[m] = x_P_update[m]