Generating repeatedly updating graph (FuncAnimation - Matplotlib)

Question

I am trying to write a code that will generate a graph that is being repeatedly updated and has twin axes (2 y-axis, sharing the same x-axis).

The code works well when I don't combine it with FuncAnimation, however when I try to do that I get an empty graph.

def animate(i):
    data=prices(a,b,c)    #function that gives a DataFrame with 2 columns and index
    plt.cla()   
    fig=plt.figure()
    ax = fig.add_subplot(111)
    ax.plot(data.index, data.value1)
    ax2 = ax.twinx()
    ax2.plot(data.index, data.value2)
    plt.gcf().autofmt_xdate()     
    plt.tight_layout()  

call = FuncAnimation(plt.gcf(), animate, 1000)  
plt.tight_layout()
plt.show
'''


I believe the error is in "call". Unfortunately, I don't know FuncAnimation so well.

Answer 1

You can try something like this:

import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
import pandas as pd
from datetime import datetime, timedelta

def getPrices(i):
    return pd.DataFrame(index=[datetime.now() + timedelta(hours=i) for i in range(10)], data={'value1':range(10), 'value2':[(x + i) % 5 for x in range(10)]})

def doAnimation():
    fig=plt.figure()
    ax = fig.add_subplot(111)

    def animate(i):
        #data=prices(a,b,c)    #function that gives a DataFrame with 2 columns and index
        data = getPrices(i)

        plt.cla()
        ax.plot(data.index, data.value1)
        ax2 = ax.twinx()
        ax2.plot(data.index, data.value2)
        plt.gcf().autofmt_xdate()     
        plt.tight_layout()  
        return ax, ax2

    call = FuncAnimation(plt.gcf(), animate, 1000)  
    plt.show()

doAnimation()

UPDATE :

Though this works in my environment, OP in a comment indicated it doesn't work and the following warning is raised:

UserWarning: Animation was deleted without rendering anything. This is most likely not intended. To prevent deletion, assign the Animation to a variable, eg anim, that exists until you have outputted the Animation using plt.show() or anim.save()

As plt.show() is called immediately after the call to FuncAnimation() , this is puzzling, but perhaps the following will help to ensure the Animation does not get deleted prematurely:

import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
import pandas as pd
from datetime import datetime, timedelta

def getPrices(i):
    return pd.DataFrame(index=[datetime.now() + timedelta(hours=i) for i in range(10)], data={'value1':range(10), 'value2':[(x + i) % 5 for x in range(10)]})

def doAnimation():
    fig=plt.figure()
    ax = fig.add_subplot(111)

    def animate(i):
        #data=prices(a,b,c)    #function that gives a DataFrame with 2 columns and index
        data = getPrices(i)

        plt.cla()
        ax.plot(data.index, data.value1)
        ax2 = ax.twinx()
        ax2.plot(data.index, data.value2)
        plt.gcf().autofmt_xdate()     
        plt.tight_layout()  
        return ax, ax2

    call = FuncAnimation(plt.gcf(), animate, 1000)  
    return call

callSave = doAnimation()
plt.show()