Matplotlib animation with blit -- how to update plot title?

Question

I use matplotlib to animate a plot, by copying the background and blitting:

f = Figure(tight_layout=True)
canvas = FigureCanvasTkAgg(f, master=pframe)
canvas.get_tk_widget().pack()
ax = f.add_subplot(111)
# Set inial plot title
title = ax.set_title("First title")
canvas.show()
# Capture the background of the figure
background = canvas.copy_from_bbox(ax.bbox)
line, = ax.plot(x, y)
canvas._tkcanvas.pack()

Periodically I update the plot:

# How to update the title here?
line.set_ydata(new_data)
ax.draw_artist(line)
canvas.blit(ax.bbox)

How could I update -- as efficiently as possible, the plot title every time I update the plot?

Edit:

title.set_text("New title")
ax.draw_artist(title)

either before or after

canvas.blit(ax.bbox)

does not update the title. I think somehow I should redraw the title artist, or I should only capture the graph, as blit(ax.bbox) overwrites the entire title plot area including the title.

Tuscan

You can use title.set_text("Second title") to update the title. – Lakisha

@Ed Smith Unfortunately title.set_text("Second title") does not update the title, probably the title text artist should be redrawn? – Tuscan

Hi @Eugen Epure, you do need to redraw, I've added an answer with minimal example to show this – Lakisha

Answer 1

Swooping in years later to say that I too was stuck on this problem for the last few days, and disabling blit wasn't an option for me (as the fps would become way too slow). For matplotlib 3.1.3 at least, if you send a resize event to the canvas, it properly flushes the background and regenerates it with any updates. So you can work around this by detecting when you need to update the title, and then calling fig.canvas.resize_event() to force a flush. Hope this helps future people!

Thremmatology

Answer 2

The following draws the plot and allows you to make changes,

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots(1,1)
ax.plot(np.linspace(0.,10.,100))
title = ax.set_title("First title")
plt.show(block=False)

The title can then be updated using,

title.set_text("Second title")
plt.draw()

Lakisha

Thanks! Of course this works, but plt.draw() is very inefficient. I try to copy the background and use canvas.blit(ax.bbox) (this updates the plot at least 10-20 times faster), the problem is the title is not updated in this case, even if I call ax.draw_artist(title) . – Tuscan

Hi @Eugen Epure, I'd guess blit doesn't assume the title will be change. It may be better to use text with title = plt.text(5,11,'Second title') to specify the title manually and then update this. I would think blitting works with text objects. – Lakisha