Matplotlib Animation does not update within class

Question

I'm writing a simple class to plot a sensor value in real-time; however, the animation does not run within the class.

I've tried to return the animation object to have an instance outside of the class but this does not work.

To my understanding, this is the same issue as raised in GitHub #1656

import datetime as dt
import matplotlib.pyplot as plt
import matplotlib.animation as animation
from random import random


class Animate:

    def __init__(self, sensor):
        # Create figure for plotting
        self.fig = plt.figure()
        self.ax = self.fig.add_subplot(1, 1, 1)
        self.xs = []
        self.ys = []
        self.ylabel = sensor
        self.readings = 20

    # This function is called periodically from FuncAnimation
    def _update(self, i, xs, ys):

        # Get sensor value
        value = random()

        # Add x and y to lists
        self.xs.append(dt.datetime.now().strftime('%H:%M:%S.%f'))
        self.ys.append(value)

        # Limit x and y lists to 20 items
        self.xs = self.xs[-self.readings:]
        self.ys = self.ys[-self.readings:]

        # Draw x and y lists
        self.ax.clear()
        self.ax.plot(xs, ys)

        # Format plot
        plt.xticks(rotation=45, ha='right')
        plt.subplots_adjust(bottom=0.30)
        plt.title(self.ylabel + ' over Time')
        plt.ylabel(self.ylabel)

    def start(self):
        print('Starting')
        # Set up plot to call animate() function periodically
        self.anim = animation.FuncAnimation(self.fig, self._update, fargs=(self.xs, self.ys), interval=200)
        plt.show();


rand = Animate('Torque')
rand.start(); 

Answer 1

your variables xs and ys are already named self.xs and self.ys, which are accessible in the class namespace; you do not need to pass them to self.update

import datetime as dt
import matplotlib.pyplot as plt
import matplotlib.animation as animation
from random import random


class Animate:

    def __init__(self, sensor):
        # Create figure for plotting
        self.fig = plt.figure()
        self.ax = self.fig.add_subplot(1, 1, 1)
        self.xs = []
        self.ys = []
        self.ylabel = sensor
        self.readings = 20

    # This function is called periodically from FuncAnimation
    def _update(self, i):

        # Read temperature (Celsius) from TMP102
        temp_c = random()

        # Add x and y to lists
        self.xs.append(dt.datetime.now().strftime('%H:%M:%S.%f'))
        self.ys.append(temp_c)

        # Limit x and y lists to 20 items
        self.xs = self.xs[-self.readings:]
        self.ys = self.ys[-self.readings:]

        # Draw x and y lists
        self.ax.clear()
        self.ax.plot(self.xs, self.ys)

        # Format plot
        plt.xticks(rotation=45, ha='right')
        plt.subplots_adjust(bottom=0.30)
        plt.title(self.ylabel + ' over Time')
        plt.ylabel(self.ylabel)

    def start(self):
        print('Starting')
        # Set up plot to call animate() function periodically
        self.anim = animation.FuncAnimation(self.fig, self._update, interval=200)
        plt.show()


rand = Animate('Torque')
rand.start()