Matplotlib is a plotting library written in Python that can be used to create line plots. By default, all the lines are drawn with a solid line.
To set a line style assign it to the named argument linestyle in the call to pyplot.plot():
matplotlib.pyplot.plot( ..., linestyle="--" )
The list of all supported line styles and their usage can be found here.
Tried with: Matplotlib 1.2, Python 3.2.3 and Windows 7 x64