Python: How to Display Annotations in Matplotlib Plots

The reason why the annotation is not displayed in the generated plot is because the plt.text() function is called after the plt.show() function. In order to display the annotation in the plot, you need to call the plt.text() function before calling plt.show(). Here's the modified code:

# ...

ZZ = results.params[0]+data.lnk*data.lnk*results.params[1]+data.lnk*results.params[2]+data.lnl*results.params[3]+data.lnk*data.lnl*results.params[4]+data.lnl*data.lnl*results.params[5]
R2 = calculate_r_squared(data.lny,ZZ )

fig = plt.figure()
plt.xlabel('Year')
plt.ylabel('Output logarithm')
plt.plot(data.year,ZZ,label='Fitted value')
plt.plot(data.year,data.lny,label='Actual value')
plt.legend()

plt.text(4, 5, r'$R^2 = $' + str(R2), fontsize=12, color='red')
plt.show()

By placing the plt.text() function before the plt.show() function, the annotation will be displayed in the generated plot.