How to pass arguments to animation.FuncAnimation()?

Question

How to pass arguments to animation.FuncAnimation()? I tried, but didn't work. The signature of animation.FuncAnimation() is

class matplotlib.animation.FuncAnimation(fig, func, frames=None, init_func=None, fargs=None, save_count=None, **kwargs) Bases: matplotlib.animation.TimedAnimation

I have pasted my code below. Which changes I have to make?

import matplotlib.pyplot as plt
import matplotlib.animation as animation

def animate(i,argu):
    print argu

    graph_data = open('example.txt','r').read()
    lines = graph_data.split('\n')
    xs = []
    ys = []
    for line in lines:
        if len(line) > 1:
            x, y = line.split(',')
            xs.append(x)
            ys.append(y)
        ax1.clear()
        ax1.plot(xs, ys)
        plt.grid()

ani = animation.FuncAnimation(fig,animate,fargs = 5,interval = 100)
plt.show()

Answer 1

Check this simple example:

# -*- coding: utf-8 -*-
import matplotlib.pyplot as plt 
import matplotlib.animation as animation
import numpy as np

data = np.loadtxt("example.txt", delimiter=",")
x = data[:,0]
y = data[:,1]

fig = plt.figure()
ax = fig.add_subplot(111)
line, = ax.plot([],[], '-')
line2, = ax.plot([],[],'--')
ax.set_xlim(np.min(x), np.max(x))
ax.set_ylim(np.min(y), np.max(y))

def animate(i,factor):
    line.set_xdata(x[:i])
    line.set_ydata(y[:i])
    line2.set_xdata(x[:i])
    line2.set_ydata(factor*y[:i])
    return line,line2

K = 0.75 # any factor 
ani = animation.FuncAnimation(fig, animate, frames=len(x), fargs=(K,),
                              interval=100, blit=True)
plt.show()

First, for data handling is recommended to use NumPy, is simplest read and write data.

Isn't necessary that you use the "plot" function in each animation step, instead use the set_xdata and set_ydata methods for update data.

Also reviews examples of the Matplotlib documentation: http://matplotlib.org/1.4.1/examples/animation/.

Answer 2

Intro

Below you will find an example of code how to pass an argument properly to the animation.funcAnimation function.

If you save all the code parts below as a single .py file you can call the script as follow in your terminal: $python3 scriptLiveUpdateGraph.py -d data.csv where data.csv is your data file containing data you want to display live.

The usual modules import

Below is my script starting:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import argparse
import time
import os

fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)

Some function

Here I declare the function that will be called later by the animation.funcAnimation function.

def animate(i, pathToMeas):
    pullData = open(pathToMeas,'r').read()
    dataArray = pullData.split('\n')
    xar = []
    yar = []
    colunmNames = dataArray[0].split(',')
    # my data file had this structure:
    #col1, col2
    #100, 500
    #95, 488
    #90, 456
    #...
    # and this data file can be updated when the script is running
    for eachLine in dataArray[1:]:
        if len(eachLine) > 1:
           x, y = eachLine.split(',')
           xar.append(float(x))
           yar.append(float(y))

   # convert list to array
   xar = np.asarray(xar)
   yar = np.asarray(yar)

   # sort the data on the x, I do that for the problem I was trying to solve.
   index_sort_ = np.argsort(xar)
   xar = xar[index_sort_]
   yar = yar[index_sort_]

   ax1.clear()
   ax1.plot(xar, yar,'-+')
   ax1.set_xlim(0,np.max(xar))
   ax1.set_ylim(0,np.max(yar))

Process the input parameters

To make the script more interactive I have added the possibility to read input file with argparse:

parser = argparse.ArgumentParser()
parser.add_argument("-d","--data",
                help="data path to the data to be displayed.",
                type=str)

args = parser.parse_args()

Call the function to do the animation

And know we are answering the main question of this thread:

ani = animation.FuncAnimation(fig, animate, fargs=(args.data,), interval=1000 )
plt.show()