Autoscale a matplotlib Axes to make room for legend

Question

I am plotting a 2D view of a spacecraft orbit using matplotlib. On this orbit, I identify and mark certain events, and then list these events and the corresponding dates in a legend. Before saving the figure to a file, I autozoom on my orbit plot, which causes the legend to be printed directly on top of my plot. What I would like to do is, after autoscaling, somehow find out the width of my legend, and then expand my xaxis to "make room" for the legend on the right side of the plot. Conceptually, something like this;

# ... code that generates my plot up here, then:
ax.autoscale_view()
leg = ax.get_legend()
leg_width = # Somehow get the width of legend in units that I can use to modify my axes
xlims = ax.get_xlim()
ax.set_xlim( [xlims[0], xlims[1] + leg_width] )
fig.savefig('myplot.ps',format='ps')

The main problem I'm having is that ax.set_xlim() takes "data" specific values, whereas leg.get_window_extent reports in window pixels (I think), and even that only after the canvas has been drawn, so I'm not sure how I can get the legend "width" in a way that I can use similar to above.

Answer 1

You can save the figure once to get the real legend location, and then use transData.inverted() to transform screen coordinate to data coordinate.

import pylab as pl
ax = pl.subplot(111)
pl.plot(pl.randn(1000), pl.randn(1000), label="ok")
leg = pl.legend()

pl.savefig("test.png") # save once to get the legend location

x,y,w,h = leg.get_window_extent().bounds

# transform from screen coordinate to screen coordinate
tmp1, tmp2 = ax.transData.inverted().transform([0, w])
print abs(tmp1-tmp2) # this is the with of legend in data coordinate

pl.savefig("test.png")