Python3x + MatPlotLib - Updating a chart?

Question

I am new to both the python and matplotlib languages and working on something for my husband.

I hope you guys can help me out.

I would like to pull in a file using Open, read it, and update a graph with it's values.

Sounds easy enough right? Not so much in practice.

Here is what I have so far to open and chart the file. This works fine as it is to chart the file 1 time.

import matplotlib.pyplot as plt
fileopen = open('.../plotresults.txt', 'r').read()
fileopen = eval(fileopen) ##because the file contains a dict and security is not an issue.
print(fileopen)  ## So I can see it working
for key,value in fileopen.items():
    plot1 = value
    plt.plot(plot1, label=str(key))
plt.legend()
plt.show()

Now I would like to animate the chart or update it so that I can see changes to the data. I have tried to use matplotlib's animation feature but it is advanced beyond my current knowledge.

Is there a simple way to update this chart, say every 5 minutes?

Note: I tried using Schedule but it breaks the program (maybe a conflict between schedule and having matplotlib figures open??).

Any help would be deeply appreciated.

nepix32 · Accepted Answer · 2014-06-03 15:29:19Z

1

Unfortunately you will just waste time trying to get a clean solution without either using matplotlib's animation feature or using the matplotlib OO interface.

As a dirty hack you can use the following:

from threading import Timer

from matplotlib import pyplot as plt
import numpy

# Your data generating code here
def get_data():
    data = numpy.random.random(100)
    label = str(data[0]) # dummy label
    return data, label

def update():
    print('update')
    plt.clf()
    data, label = get_data()
    plt.plot(data, label=label)
    plt.legend()
    plt.draw()
    t = Timer(0.5, update) # restart update in 0.5 seconds
    t.start()

update()
plt.show()

It spins off however a second thread by Timer. So to kill the script, you have to hit Ctrl-C twice on the console.

I myself would be interested if there is a cleaner way to do this in this simple manner in the confines of the pyplot machinery.

Edits in italic.

edited Jun 3, 2014 at 15:29

answered Jun 3, 2014 at 12:25

nepix32

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2 Comments

tacaswell Over a year ago

It would be better to explicitly get a reference to and Axes object and us the OO interface, rather than rely on the pyplot state machine.

nepix32 Over a year ago

This example shall check how far one can get with the pyplot machinery. Regarding the OO interface: Explain that to the thread opener :). Edited my answer.

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