在iPython笔记本中动态更新绘图

Question

As referred in this question , I am trying to update a plot dynamically in an iPython notebook (in one cell). The difference is that I don't want to plot new lines, but that my x_data and y_data are growing at each iteration of some loop.

What I'd like to do is:

import numpy as np
import time
plt.axis([0, 10, 0, 100]) # supoose I know what the limits are going to be
plt.ion()
plt.show()
x = []
y = []
for i in range(10):
     x = np.append(x, i)
     y = np.append(y, i**2)
     # update the plot so that it shows y as a function of x
     time.sleep(0.5) 

but I want the plot to have a legend, and if I do

from IPython import display
import time
import numpy as np
plt.axis([0, 10, 0, 100]) # supoose I know what the limits are going to be
plt.ion()
plt.show()
x = []
y = []
for i in range(10):
    x = np.append(x, i)
    y = np.append(y, i**2)
    plt.plot(x, y, label="test")
    display.clear_output(wait=True)
    display.display(plt.gcf())
    time.sleep(0.3)
plt.legend()

I end up with a legend which contains 10 items. If I put the plt.legend() inside the loop, the legend grows at each iteration... Any solution?

Answer 1

Currently, you are creating a new Axes object for every time you plt.plot in the loop.

So, if you clear the current axis ( plt.gca().cla() ) before you use plt.plot , and put the legend inside the loop, it works without the legend growing each time:

import numpy as np
import time
from IPython import display

x = []
y = []
for i in range(10):
    x = np.append(x, i)
    y = np.append(y, i**2)
    plt.gca().cla() 
    plt.plot(x,y,label='test')
    plt.legend()
    display.clear_output(wait=True)
    display.display(plt.gcf()) 
    time.sleep(0.5) 

EDIT: As @tcaswell pointed out in comments, using the %matplotlib notebook magic command gives you a live figure which can update and redraw.