Informatics2-2018/Lab07

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Exercises

Work in Spyder!

Shapes on a canvas

Shapes

Write a class called Shape.

• Let it have two members: x and y, the coordinates of the shape on the plane (center of mass).
• Define a move method, with one parameter v: a list of length 2, a vector to translate the shape with. After this method the coordinates should be changed.

Define the following classes as children of Shape:

• Ellipse with additional parameters (except the (x, y) coordinates): a and b the x and y axes radii
• Rectangle with additional parameters (except the (x, y) coordinates) a and b the length of the sides

Write an area method for both, which calculates the area!

Define an equation method for printing the equation of the Ellipse! Something like:

   ((x-1)/2)^2 + ((y-2)/3)^2 = 1

Inheritance and constructors

If the child class (e.g. Ellipse) you want to call the parents class' constructor then you have two ways:

   class B(A):
       def __init__(self, x, y, a, b):
            A.__init__(self, x, y)
            # OR
            super(B, self).__init__(x, y)

The first explicitly calls the parents __init__

   A.__init__(self, x, y)

The second one calls the parent of B which happens to be A:

   super(B, self).__init__(x, y)

Canvas

Define a class called Canvas (vászon)

• Its only member variable should be a list of Shapes: shapes. This stores several Shape objects.
• Define an add method which adds a new shape to the canvas!
• Make this class iterable! Write the __iter__(self) and the next(self) methods, as seen on the lecture.
• Define a crop method in the following way.
  • Its two parameters should be two coordinates: a top-left corner and a bottom-right corner.
  • The function should return the list of Shapes which entirely fit in that rectangle.
  • For this it is best to implement a box() method on both Ellipse and Rectangle which returns a bounding box of the shape:

a list of two coordinates, the top-left corner and a bottom-right corner of the object.

Iterables

Write an iterable class like range, but without returning a whole list, but storing only the actual element.

class Range(object):
    def __init__( ... ):
        ...
    def __iter__( ... ):
        ...
    def next( ... ):
        ...

• Its constructor should have one parameter: a number or a string. The iteration should go up that number, from 0 with 1 steps.
• If the number is not positive, then the iteration should take 0 steps.
• If you get a string then try to convert it to a number. It it cannot be converted, then raise a ValueError exception.
  • If it is a valid integer, then calculate with that.
• If you get the string "inf" then make the iteration go endless (infinite loop)!

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