Force equal axes scales

[tedsteiner]

Is there a way to force the x and y axes to have equal scales? I have been computing the correct pixel heights and widths for a figure based on xlim and ylim. It would be nice to be able to write:

figure(name="Figure Name", width=width, aspect_ratio=1)

rather than:

xrange = x_max - x_min
yrange = y_max - y_min
aspect_ratio = xrange / yrange
height = int( width / aspect_ratio )
figure(name="Figure Name", width=width, height=height)