Python Programming- Defining a Class

Question

This is the problem,

Define the class Rectangle. It's constructor takes a pair of numbers representing the top-left corner, and two other numbers representing the width and height. It has the following methods:

get_bottom_right() - return the bottom right corner as a pair of numbers. move(p) - move the rectangle so that p becomes the top-left corner (leaving the width and height unchanged). resize(width, height) - set the width and height of the rectangle to the supplied arguments (leaving the top-left corner unchanged). __str__() - return the string representation of the rectangle as a pair of pairs - i.e. the top left and bottom right corners.

Note: Unlike the co-ordinate system you may have encountered before, y, in this question, increases as you move vertically downwards.

Examples: Each example below follows on from the previous one. Be careful to get the spacing right for str - i.e. comma followed by space.

r = Rectangle((2,3), 5, 7)
str(r)
*'((2, 3), (7, 10))'*
r.move((5,6))
str(r)
'((5, 6), (10, 13))'
r.resize(2,3)
str(r)
*'((5,6), (7, 9))'*
r.get_bottom_right()
*(7, 9)*

This is my answer:

class Rectangle():
 def __init__(self, coords, sizex, sizey):
 self._startx, self._starty = coords
 self._sizex = sizex
 self._sizey = sizey
 def get_bottom_right(self):
 print '(%s, %s)' % (self._startx + self._sizex, self._starty + self._sizey)
 def move(self, pos):
 self._startx, self._starty = pos
 def resize(self, width, height):
 self._sizex = width
 self._sizey = height
 def __str__(self):
 return '((%s, %s), (%s, %s))' % (self._startx, self._starty, self._startx + self._sizex, self._starty + self._sizey)
r = Rectangle((2, 3), 5, 7)
str(r)
r.move((5,6))
str(r)
r.resize(2,3)
str(r)
r.get_bottom_right()

I got the correct answer but the homeowork system says im wrong.

Wrong: the Rectangle class should inherit from the object class

can anyone tell me where im wrong?

Answer 1

You are looking for,

class Rectangle(object):
...

This is a new-style class. Read more in this SO post: What is the difference between old style and new style classes in Python?

I also have a feeling that your homework system is using pylint to verify/grade your code. You might want to stick to PEP8 standards.

• RvdK: (object) is indeed the new style
• bboychua: I have changed to Rectangle(object), but why does my answer changes as well. It was (7,9) and it is (14,11) now. what is happening....
• ComputerFellow: @bboychua Check if you've changed the numbers by mistake? There is no way inheriting object is affecting it.
• bboychua: okay this is what happened. if I use Rectangle(), I get (7,9), and if I use Rectangle(object), I get different answers everytime.

Answer 2

Another error in your Rectangle class is that the get_bottom_right() method is supposed to return a tuple, not print it. Of course, returning a tuple in the interpreter without assigning it will cause it to be printed.