CSC111 Example of Inheritance: Rectangle with a label

--D. Thiebaut 08:36, 8 December 2011 (EST)

---

# myRectangles.py
# D. Thiebaut
# Demonstration of inheritance with Python Classes
# In this program myRect inherits from Rectangle.
# Rectangle is the base class
# myRect is the derived class
# it adds a label in the center of the rectangle
 
from graphics import *
import time
 
class myRect( Rectangle ):
    """Derived class for a rectangle with a label in it"""
 
    def __init__( self, P1, P2, label="Unknown" ):
        """Constructor for the class"""

        #--- initializes the base class ---
        Rectangle.__init__( self, P1, P2 )
 
        #--- puts the lable in the middle ---
        x1 = P1.getX()
        y1 = P1.getY()
        x2 = P2.getX()
        y2 = P2.getY()
        self.label = Text( Point( (x1+x2)/2, (y1+y2)/2 ), label )
 
    def draw( self, win ):
        """ draws the rectangle and the label """
        Rectangle.draw( self, win )
        self.label.draw( win )
 
    def move( self, dx, dy ):
        Rectangle.move( self, dx, dy )
        self.label.move( dx, dy )        
 
 
def main():
    """displays the graphics window and an instance of myRect"""
    win = GraphWin( "Inheritance", 400, 400 )
    r = myRect( Point( 20,20 ), Point( 150, 50 ), "Hello there!" )
    r.draw( win )

    #--- animation loop ---
    while True:
         r.move( random.choice( [-2, -1, 0, 1, 2 ] ), 0 )
 
         if win.checkMouse() != None:
             break

    win.close()
 
main()