[matpltlib]Basic question about callback function

[Yoriz]

When the slider is altered it triggers an event that calls the connected event handler with the val of the slider,
that is why the event handler function must except the val argument.
To access val in the event handler function just use the val attribute like shown below.

sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0, valstep=delta_f)
sfreq.on_changed(update)
 
def update(val):
    print(val)