Unlike 'plot', 'plot_date' does not completely honor
the linestyle specification if given in a dictionary.
Try this:
import pylab
l=dict(linestyle='-')
pylab.plot_date([100000,200000,300000],[1,2,3],**l)
You will see points as well as lines plotted.
I suspect a small bug here?
Thanks,
Alan Isaac
using 0.83.2