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You can easily plot a segment between two suitable points on the line passing by P and R. For example, you can replace plotE += line([P.xy(),R.xy()],color='red') by:

vP, vR = vector(P.xy()), vector(R.xy())
PR = (vR - vP).normalized()
plotE += line([vP-5*PR, vP+4*PR], color="red")