How to insert a line into a gnuplot py chart?

Question

I want to insert a line in the middle of a graph I’m filling with Gnuplot (python),which will serve as Threshold, as for example in y = 0. How can I do this?

Answer 1

I figured out the way.

Just include an arrow, counting the initial and final position, and finally saying that it need not have tip, as in the example below:

g('set arrow from <initial position x,y> to <final position x,y> nohead')