Extraire un élément d'une liste

from matplotlib.pylab import axis,box,plot,text,ginput
import matplotlib.pyplot as plt
xmin=-30 ; xmax=30 ; ymin=-1 ; ymax=1 ; fp=10
axis([xmin,xmax,ymin,ymax])
box('off')
plot([xmin,xmax],[0,0],'k')
plot([0,0],[ymin,ymax],'k',linewidth=2)
if fp>0:
    plot(0,ymax*0.97,'k^',markersize=10)
    plot(0,ymin*0.97,'kv',markersize=10)
if fp<0:
    plot(0,ymin*0.97,'k^',markersize=10)
    plot(0,ymax*0.97,'kv',markersize=10)
plot(fp,0,'k+')
text(fp,ymax*.025,"F'")
plot(-fp,0,'k+')
text(-fp,ymax*.025,"F")
text(xmax*.025,ymax*.025,'O')
coord_points=ginput(1,timeout=300)
plt.draw()
plt.waitforbuttonpress()