How to add trendline in python matplotlib dot (scatter) graphs?

How could I add trendline to a dot graph drawn using matplotlib.scatter?

as explained here

With help from numpy one can calculate for example a linear fitting.

    # plot the data itself
    pylab.plot(x,y,'o')

    # calc the trendline
    z = numpy.polyfit(x, y, 1)
    p = numpy.poly1d(z)
    pylab.plot(x,p(x),"r--")
    # the line equation:
    print "y=%.6fx+(%.6f)"%(z[0],z[1])

From: stackoverflow.com/q/26447191