class Drawing:
    """Class for displaying rectangles, squares and circles.
    
    Note that origin is upper-LEFT with y positive DOWNWARDS."""

    def __init__(self, width, height):
        try:
            import Tkinter
        except ImportError:
            import tkinter as Tkinter
        self.app = Tkinter.Frame()
        self.app.grid(sticky="nsew")
        self.canvas = Tkinter.Canvas(self.app,
                        width=width, height=height)
        self.canvas.grid(row=0, column=0, sticky="nsew")

    def add_rectangle(self, llx, lly, urx, ury, color):
        self.canvas.create_rectangle((llx, lly, urx, ury), fill=color)

    def add_circle(self, llx, lly, urx, ury, color):
        self.canvas.create_oval((llx, lly, urx, ury), fill=color)

    def run(self):
        self.app.mainloop()

if __name__ == "__main__":
    # Some simple test code.
    d = Drawing(100, 100)
    d.add_circle(25, 25, 75, 75, "red")
    d.run()
    # The "real" testing code should be much more elaborate than this
    # of course.  The code here:
    # (a) does not test the entire API (add_rectangle is not
    #     used), and
    # (b) does not test each method with different data (only
    #     one good input is used; boundary conditions
    #     and error inputs are not tested).
    # A good way for constructing test code is to use the standard
    # Python "unittest" module.