Quan Nguyen《Advanced Python Programming》粒子模拟代码运行异常求助

问题背景 #

我正在阅读Quan Nguyen所著的《Advanced Python Programming》第二版，书中的粒子圆周运动模拟代码无法正常运行。使用Windows 11系统、Python 3.8.12版本，在VSCode中运行无任何反应，JupyterLab运行时出现警告。

原代码 #

# %load simul.py
from matplotlib import pyplot as plt
from matplotlib import animation
from random import uniform
import timeit
import os

os.system('cls' if os.name == 'nt' else 'clear')


class Particle:

    __slots__ = ("x", "y", "ang_speed")

    def __init__(self, x, y, ang_speed):
        self.x = x
        self.y = y
        self.ang_speed = ang_speed


class ParticleSimulator:
    def __init__(self, particles):
        self.particles = particles

    def evolve(self, dt):
        timestep = 0.00001
        nsteps = int(dt / timestep)

        for i in range(nsteps):
            for p in self.particles:

                norm = (p.x ** 2 + p.y ** 2) ** 0.5
                v_x = (-p.y) / norm
                v_y = p.x / norm

                d_x = timestep * p.ang_speed * v_x
                d_y = timestep * p.ang_speed * v_y

                p.x += d_x
                p.y += d_y


def visualize(simulator):

    X = [p.x for p in simulator.particles]
    Y = [p.y for p in simulator.particles]

    fig = plt.figure()
    ax = plt.subplot(111, aspect="equal")
    (line,) = ax.plot(X, Y, "ro")

    # Axis limits
    plt.xlim(-1, 1)
    plt.ylim(-1, 1)

    # It will be run when the animation starts
    def init():
        line.set_data([], [])
        return (line,)

    def animate(i):
        # We let the particle evolve for 0.1 time units
        simulator.evolve(0.01)
        X = [p.x for p in simulator.particles]
        Y = [p.y for p in simulator.particles]

        line.set_data(X, Y)
        return (line,)

    # Call the animate function each 10 ms
    anim = animation.FuncAnimation(fig, animate, init_func=init, blit=True, interval=10)
    plt.show()


def test_visualize():
    particles = [
        Particle(0.3, 0.5, +1),
        Particle(0.0, -0.5, -1),
        Particle(-0.1, -0.4, +3),
    ]

    simulator = ParticleSimulator(particles)
    visualize(simulator)

if __name__ == "__main__":
    test_visualize()

JupyterLab中的警告信息 #

C:\Users\ephra\AppData\Local\Temp\ipykernel_18360\3786700959.py:71: UserWarning: frames=None which we can infer the length of, did not pass an explicit *save_count* and passed cache_frame_data=True.  To avoid a possibly unbounded cache, frame data caching has been disabled. To suppress this warning either pass `cache_frame_data=False` or `save_count=MAX_FRAMES`.
  anim = animation.FuncAnimation(fig, animate, init_func=init, blit=True, interval=10)

问题解决方法 #

1. VSCode无反应问题 #

VSCode中动画窗口无法弹出，通常是matplotlib后端配置问题。可以在代码开头添加以下代码指定交互式后端：

import matplotlib
# 选择系统支持的后端，比如TkAgg或QtAgg
matplotlib.use('TkAgg')

如果系统缺少对应后端依赖（比如Tkinter），需要先安装相关组件。另外，也可以在VSCode的Python扩展设置中，将Matplotlib后端设置为"Interactive"。

2. JupyterLab警告问题 #

警告是因为FuncAnimation未指定save_count或cache_frame_data参数，新版本matplotlib为避免无限缓存触发提示。修改FuncAnimation调用，添加任意一个参数即可消除警告：

# 方式一：指定save_count
anim = animation.FuncAnimation(fig, animate, init_func=init, blit=True, interval=10, save_count=100)
# 方式二：关闭缓存
anim = animation.FuncAnimation(fig, animate, init_func=init, blit=True, interval=10, cache_frame_data=False)

额外优化 #

原代码中evolve函数的嵌套循环效率较低，可通过向量化运算优化，但这不是导致运行失败的原因，仅影响动画流畅度。

内容的提问来源于stack exchange，提问作者ezyman