Scale of the quiver does not print the actually value till after the figure pop up

This is a follow up of question on matplotlib githup

I am trying to print the value fo the automated scale being calculated by the quiver as the following:

fig, ax = plt.subplots(1,2)
axl=ax[0].quiver(x, y, U, V,  angles='uv',scale_units='width')
ax[0].set_title('scale_units=width \n scale='+str(axl.scale))
print('left figure scale '+str(axl.scale))
print('left figure scale_units '+axl.scale_units)
axr=ax[1].quiver(x, y, U, V,  angles='uv',scale_units='height')
ax[1].set_title('sacle_units=height \n scale='+str(axl.scale))
print('right figure scale '+str(axl.scale))
print('left figure scale_units '+axl.scale_units)

Yet, as printed on the console and shown in the figure title, the scale is None, which I know is not the true value.

After the figure popped up, I printed the scale again, and I got the correct answer.

print('left figure scale '+str(axl.scale))
print('right figure scale '+str(axr.scale))

I got
right figure scale 127.27922061357857
right figure scale 189.83025409097942

Is it expected that we only obtain the true scale value after the figure pops up on the scale? I understand that scale may be among the parameters that is being calculated just before the rending the figure, yet should not this value be available before popping out the figure?