MatPlotLib with ion() does not show window

Question

If I run the following code:

import matplotlib.pyplot as plt
import numpy as np

#plt.ion()

while True:
    print('loop')
    x = range(10)
    y = np.random.rand(10)
    plt.scatter(x, y)
    plt.show()

Then I see a scatter plot displayed on my screen. Then each time I close the window for the plot, it displays a new plot with new data.

However, if I uncomment the line plt.ion(), nothing is displayed at all. There is no window created, and the program just continues through the loop, printing out 'loop'.

I want to be able to display a graph, and then return to the code automatically, with the graph still displayed. How can I do this?

jwalton jwalton · Accepted Answer · 2019-02-14T19:25:31

If you want to plot on top of the same figure window, rather than generating a new window at every iteration the following will work:

import matplotlib.pyplot as plt
import numpy as np

plt.ion()

fig, ax = plt.subplots(1, 1)

while True:
    # If wanting to see an "animation" of points added, add a pause to allow the plotting to take place
    plt.pause(1)
    x = range(10)
    y = np.random.rand(10)
    ax.scatter(x, y)

The result you see will depend on the which matplotlib backend you are using. If you're wanting to see the new points being added you should use Qt4 or Qt5

MatPlotLib with ion() does not show window

1 Answers