matplotlib Button click handler inside a function doesn't work

Question

If I define a Button click handler inside a function, it doesn't work. In the following example figures f1 and f2 look the same, but only if I press the button on f2, it produces output.

from matplotlib import pyplot as plt
from matplotlib.widgets import Button

def handler(*args, **kwargs):
    print('handled')

def testfn():
    f1 = plt.figure('f1')
    b1 = Button(f1.add_axes([0.4, 0.3, 0.1, 0.04]), 'Click!')
    b1.on_clicked(handler)

f2 = plt.figure('f2')
b2 = Button(f2.add_axes([0.4, 0.3, 0.1, 0.04]), 'Click!')
b2.on_clicked(handler)

testfn()

plt.show()

ImportanceOfBeingErnest · Accepted Answer · 2018-02-01 14:26:18Z

7

As the documentation tells about just any widget,

For the button to remain responsive you must keep a reference to it.

You hence need to return the button from the function to keep the reference to it (button = testfn()), otherwise it will be garbage collected as soon as the function returns.

The example could hence look like this:

from matplotlib import pyplot as plt
from matplotlib.widgets import Button

def handler(*args, **kwargs):
    print('handled')

def testfn():
    f1 = plt.figure('f1')
    b1 = Button(f1.add_axes([0.4, 0.3, 0.1, 0.04]), 'Click!')
    b1.on_clicked(handler)
    return b1

f2 = plt.figure('f2')
b2 = Button(f2.add_axes([0.4, 0.3, 0.1, 0.04]), 'Click!')
b2.on_clicked(handler)

button = testfn()

plt.show()

answered Feb 1, 2018 at 14:26

ImportanceOfBeingErnest

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1 Comment

danelliottster Over a year ago

Solution verified utilizing a number of different widgets.

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