Update intro.py

intro.py

@@ -5,7 +5,10 @@ from matplotlib import pyplot as plt
 
 
 # display simple bar-chart
-plt.bar(['A', 'B', 'C'], [2, 6, 5], 0.9)
+x = range(3)
+y =  [2, 6, 5]
+plt.bar(x, y, 0.9)
+plt.xticks(x, ('A', 'B', 'C'))
 plt.show()
 
 # Read csv-file from disk into dataframe object