Step forward and backward frame by frame in animation in matplolib: Problem when using blit=True

Question

This answer shows an approach to implement pause and stepping frame by frame in matplotlib. However in my case I want to use blitting for performance reasons. But in this case the example doesn't work

1. Run python3 animation.py it does display an empty canvas and says (in the console) TypeError 'Text' object is not iterable
2. If I hit the right button, it shows 1. Then I can go through the numbers using left/right buttons.
3. Using space to start or stop the animation doesn't have any effect.

If I remove blit=True everything works as expected.

So how to change the example to make it work with blitting:

import matplotlib.pyplot as plt
import matplotlib.animation as ani

fig, ax = plt.subplots()
txt = fig.text(0.5,0.5,'0',fontsize=30)

def update_time():
    t = 0
    while True:
        t += anim.direction
        yield t

def update_plot(t):
    txt.set_text('%s'%t)
    return txt

def on_press(event):
    if event.key.isspace():
        if anim.running:
            anim.event_source.stop()
        else:
            anim.event_source.start()
        anim.running ^= True
    elif event.key == 'left':
        anim.direction = -1
    elif event.key == 'right':
        anim.direction = +1

    # Manually update the plot
    if event.key in ['left','right']:
        t = anim.frame_seq.__next__()
        update_plot(t)
        plt.draw()

fig.canvas.mpl_connect('key_press_event', on_press)
anim = ani.FuncAnimation(fig, update_plot, frames=update_time,interval=100,blit=True)
anim.running = True
anim.direction = +1
plt.show()