加拿大瑞尔森大学 Python习题 Lab 7

Lab 7 – CPS 106

This lab helps you get familiar with classes and inheritance.

1.   Write a class called Shape.

class Shape:

2.   The Shape class is going to represent a general shape in the 2D plane. A shape is described by a set of points that determine its boundary. Write a class called Point. The point class has two attributes x and y which are unique to each point. So we define them as instance variables, i.e., using the self object. We initialize them in the __init__ mathod.

class Point(x, y):

def __init__(self, x, y):

self.x = x

self.y = y

3.   Write  the __str__ method for the Point class. The method  should return a  string in the following format: “(x, y)”

4.   Test the point class using the following:

p = Point(31, 7)

print(p)

5.   Add the __init__ method to the shape class. In the method you should initialize the list of boundary points to empty:

self.boundary = []

6.   Add a method called set_boundary to the Shape class. The set boundary method accepts a list of points called boundary. In the method you should set self.boundary to the input boundary:

def set_boundary(boundary):

7.   Write the __str__ method for Shape. The method should return a string in the following format: “Boundary: (x1, y1), (x2, y2), ...” where the set of points are the ones in self.boundary. Hint1: remember that the point class gives you a string of the form “(x, y)”, so you can use that here. For example if self.boundary[0] is the point p = (5, 12) then str(p) is the string “(5,

12)”. Hint2: you should loop through all the points in self.boundary to get the final result.

8.   Define a class called Rectangle. The Rectangle class will be a subclass of Shape:

class Rectangle(Shape):

pass

9.   Test the rectangle class using the following. The first point is assumed to be the bottom left corner of the rectangle.

rect = Rectangle()

rect.set_boundary([Point(0, 0), Point(0, 3), Point(5, 3), Point(5, 0)])

print(rect)

10. Define a class called Square. The Square class will be a subclass of Rectangle:

class Square(Rectangle):

pass

Test the Square class using the following. The first point is assumed to be the bottom left corner of the square.

square = Square()

square.set_boundary([Point(0, 0), Point(0, 3), Point(3, 3), Point(3, 0)])

print(square)

11. Define a class called Triangle. The Triangle class will be a subclass of Shape. Test the Triangle class using the following:

trgle = Triangle()

p(t)ri(rg)t(e)tgle(set_)oundary([Point(0, 7), Point(3, 3), Point(2, 5)])

12. The diagram of the classes now looks like the following:

13. Add the following method to the Square class:

def set_side_length(length):

The argument length is an integer, based on which the new boundary point of the square will be calculated. Since the first point, i.e., p = self.boundary[0], is the bottom left corner, the point above p, i.e., self.boundary[1], will be (p.x, p.y + length). Figure out the position of the rest of the points. Test your code using the following:

square.set_side_length(5)

print(square)

代码

7-1

7-2

7-13 class