import matplotlib.pyplot as plt
from matplotlib.widgets import Slider
fig, ax = plt.subplots()
plt.subplots_adjust(left=0.25, bottom=0.25)
x = [1, 2, 3, 4, 5]
y = [i**2 for i in x]
line, = ax.plot(x, y)
axcolor = 'lightgoldenrodyellow'
ax_a = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
slider_a = Slider(ax_a, 'a', 0.1, 10.0, valinit=1)
def update(val):
a = slider_a.val
y_new = [a * i**2 for i in x]
line.set_ydata(y_new)
fig.canvas.draw_idle()
slider_a.on_changed(update)
plt.show()