title: Python realtime plotting
body: <p>I acquire some data in two arrays: one for the time, and one for the value. When I reach 1000 points, I trigger a signal and plot these points (x=time, y=value).</p>
  
  <p>I need to keep on the same figure the previous plots, but only a reasonable number to avoid slowing down the process. For example, I would like to keep 10,000 points on my graph.
  The matplotlib interactive plot works fine, but I don't know how to erase the first points and it slows my computer very quickly.
  I looked into matplotlib.animation, but it only seems to repeat the same plot, and not really actualise it.</p>
  
  <p>I'm really looking for a light solution, to avoid any slowing.</p>
  
  <p>As I acquire for a very large amount of time, I erase the input data on every loop (the 1001st point is stored in the 1st row and so on).</p>
  
  <p>Here is what I have for now, but it keeps all the points on the graph:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  
  def init_plot():
    plt.ion()
    plt.figure()
    plt.title("Test d\'acqusition", fontsize=20)
    plt.xlabel("Temps(s)", fontsize=20)
    plt.ylabel("Tension (V)", fontsize=20)
    plt.grid(True)
  
  def continuous_plot(x, fx, x2, fx2):
    plt.plot(x, fx, 'bo', markersize=1)
    plt.plot(x2, fx2, 'ro', markersize=1)
    plt.draw()
  </code></pre>
  
  <p>I call the init function once, and the continous_plot is in a process, called every time I have 1000 points in my array.</p>