comment this code line by line: 
# Plot sigmoid(z) over a range of values from -10 to 10
z = np.arange(-10,11)

fig,ax = plt.subplots(1,1,figsize=(8,3))
# Plot z vs sigmoid(z)
ax.plot(z, sigmoid(z), c="b")

ax.set_title("Sigmoid function")
ax.set_ylabel('sigmoid(z)')
ax.set_xlabel('z')
draw_vthresh(ax,0) Do not include the following keywords: z, code, fig, plt.subplots(1,1,figsize=(8,3
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