set_data and autoscale_view matplotlib

I have multiple lines to be drawn on the same axes, and each of them are dynamically updated (I use set_data), The issue being that i am not aware of the x and y limits of开发者_JS百科 each of the lines. And axes.autoscale_view(True,True,True) / axes.set_autoscale_on(True) are not doing what they are supposed to. How do i auto scale my axes?

import matplotlib.pyplot as plt

fig = plt.figure()
axes = fig.add_subplot(111)

axes.set_autoscale_on(True)
axes.autoscale_view(True,True,True)

l1, = axes.plot([0,0.1,0.2],[1,1.1,1.2])
l2, = axes.plot([0,0.1,0.2],[-0.1,0,0.1])

#plt.show() #shows the auto scaled.

l2.set_data([0,0.1,0.2],[-1,-0.9,-0.8])

#axes.set_ylim([-2,2]) #this works, but i cannot afford to do this.  

plt.draw()
plt.show() #does not show auto scaled

I have referred to these already, this , this. In all cases I have come across, the x,y limits are known. I have multiple lines on the axes and their ranges change, keeping track of the ymax for the entire data is not practical

A little bit of exploring got me to this,

xmin,xmax,ymin,ymax = matplotlib.figure.FigureImage.get_extent(FigureImage) 

But here again, i do not know how to access FigureImage from the Figure instance.

Using matplotlib 0.99.3

From the matplotlib docs for autoscale_view:

The data limits are not updated automatically when artist data are changed after the artist has been added to an Axes instance. In that case, use matplotlib.axes.Axes.relim() prior to calling autoscale_view.

So, you'll need to add two lines before your plt.draw() call after the set_data call:

axes.relim()
axes.autoscale_view(True,True,True)