# 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)!

## Chess

Define a class called Piece. This will represent a chess piece (a figure on the chessboard). Store its position and its color (Black/White) and its __str__ function should write the position like A2, G3 etc. Store the position as integers.

• Define child classes King and Pawn!
• Implement their __str__ method which also prints the type of the figure. (You can implement it in the parent class, too)
• Every child class should have a .move(pos) method, where pos is a string like A3, G2 etc. Move the piece to that position if it is accepted by the chess rules. If the move was successful return True otherwise False!
• Define a PieceMoveError exception. If the move is not allowed, then raise this exception!

Implement the Board class. Store the list of figures.

• Make an add method which puts a figure on the table.
• Implement a move(pos1, pos2) method in Board which moves a figure from one position to the other, if the move is allowed (handle the PieceMoveError exception).
• Mind that there may be an other figure on the pos2 position. If the target position is occupied with the same player's figure, then the move is not allowed. If the target is the other player's figure, then remove their figure and replace it with the new figure (its a capture).
• Its easier if you implement an .occupied(pos) method first, which tells whether a given position is occupied or not.
• Implement the other pieces: Knight, Rook, Bishop and Queen!
• Start with the Rook, its move is the simplest. Mind that the figure cannot pass through existing figures!
• Implement the Knight class! The Knight and Queen can jump through other figures, so its not a problem for them.
• After the bishop its not hard to implement Queen.
• Define a check method in Board. Return the color of the player who's King is in a chess position, or empty string of there is no chess position!
• Modify the Board's move method not to allow self-checks (when the active player makes its own King into a chess)!
• Implement the __str__ method of Board!

After all these, implement the start method which assigns the board to a starting position.

### CLI

• Make a chess game in command line: read the moves of the players with raw_input and print the board after each step. The white player starts and mind that the same player cannot move twice.
• Try it from command line