X = np.linspace(-2 * np.pi, 2 * np.pi, 70)
F1 = np.sin(X)
F2 = 3 * np.sin(X)
ax = gca() # get the current axes, creating one if necessary
ax.spines['top'].set_color('none')
ax.spines['right'].set_color('none')
ax.xaxis.set_ticks_position('bottom')
ax.spines['bottom'].set_position(('data',0))
ax.yaxis.set_ticks_position('left')
ax.spines['left'].set_position(('data',0))
plot(X, F1)
plot(X, F2)
show()