CODE EXAMPLE FOR PYTHON

horizontal line to the y axis in matplotlib

# importing the module
import matplotlib.pyplot as plt
  
# plotting line within the given range
plt.axhline(y = .5, xmin = 0.25, xmax = 0.9)
  
# line colour is blue
plt.axhline(y = 3, color = 'b', linestyle = ':', label = "blue line")
  
# line colour is white
plt.axhline(y = 1, color = 'w', linestyle = '--', label = "white line")
  
# line colour is red
plt.axhline(y = 2, color = 'r', linestyle = 'dashed', label = "red line")    
    
# adding axis labels    
plt.xlabel('x - axis')
plt.ylabel('y - axis')
  
# plotting the legend
plt.legend(bbox_to_anchor = (1.0, 1), loc = 'upper center')
  
# displaying the plot
plt.show()