matplotlib动画在运行后立即关闭

Question

我正在尝试制作一个向左或向右移动的小粒子动画，但该图形在运行后立即关闭。我尝试在论坛上阅读一些提示，但没有帮助。
无法理解为什么动画对我不起作用。
我看了一些例子，但没有发现我犯的错误。 你能帮我吗？

    import numpy as np
    import random
    from scipy.spatial.distance import pdist, squareform

    import matplotlib.pyplot as plt
    import scipy.integrate as integrate
    import matplotlib.animation as animation

    class ParticleBox:
       """

    init_state is a 3D array of x,y coordinates + probability to go left or right

    bounds is the size of the box: [xmin, xmax, ymin, ymax]
    """
    def __init__(self,
                 init_state,   bounds = [-9, 9, -2, 2],
                 size = 0.04, step_size=0.05):
        self.init_state = np.asarray(init_state, dtype=float)

        self.size = size
        self.state = self.init_state.copy()
        self.time_elapsed = 0
        self.bounds = bounds
        self.ycorbeg=range(len(self.state))

    def step(self, dts):
        pr=0.4
        pl=0.4
        ps=0.2

        self.time_elapsed+=dts

        for i in range(len(self.state)):
            print c
            c=random.random()
            if c<pr:
                print c
                self.state[i,2]=ze
            elif (pr<=c and c<pr+pl):
                self.state[i,2]=-step_size
            else:
                self.state[i,0]=self.state[i,0]
        self.state[:, 0] += dt * self.state[:, 2]
    np.random.seed(0)                    
    beginx=np.random.rand(1000)-0.5
    lenbegin=len(beginx)
    def beginy(lenbegin,maxy=250):
    i=0
    beginy=np.zeros(lenbegin)
    while i<lenbegin:
        for j in range(int(-maxy/2),int(maxy/2)):
            beginy[i]=j/50.0
            i+=1
    if len(beginx)==len(beginy):
        ze=np.zeros(len(beginy))
        print zip(beginx,beginy,ze)[0]
        return zip(beginx,beginy,ze)
    else:
        raise ValueError

    init_state=beginy(lenbegin)
    box = ParticleBox(init_state)



    dts = 1. / 30
#------------------------------------------------------------
# set up figure and animation
    fig = plt.figure()
    fig.subplots_adjust(left=0, right=1, bottom=0, top=1)
    ax = fig.add_subplot(111, aspect='equal',         autoscale_on=False,
                     xlim=(-3.2, 3.2), ylim=(-2.4, 2.4))

# particles holds the locations of the particles
    particles, = ax.plot([], [], 'bo', ms=6)

# rect is the box edge
    rect = plt.Rectangle(box.bounds[::2],
                     box.bounds[1] - box.bounds[0],
                     box.bounds[3] - box.bounds[2],
                     ec='none', lw=2, fc='none')
    ax.add_patch(rect)

    def init():
    """initialize animation"""
    global box, rect
    particles.set_data([], [])
    rect.set_edgecolor('none')

    return particles, rect

    def animate(i):
    """perform animation step"""
    global box, rect, dts,  fig
    box.step(dts)

    ms = int(fig.dpi * 2 * box.size *     fig.get_figwidth()
             / np.diff(ax.get_xbound())[0])

    # update pieces of the animation
    rect.set_edgecolor('k')

    particles.set_data(box.state[:, 0], box.state[:, 1])
    particles.set_markersize(ms)
    return particles, rect

    anim = animation.FuncAnimation(fig, animate, frames=600,
                              interval=10, blit=True, init_func=init)



    plt.show()