Expand ch10-3 solution

Author: dbader

ch10-primer-on-oop/3-inherit-from-other-classes.py

@@ -41,4 +41,7 @@ def __init__(self, side_length):
 
 
 square = Square(4)
-print(square.area())
+print(square.area()) # 16
+
+square.width = 5 # Modifies .width but not .length
+print(square.area()) # 20