Lab 11 - Grid

Due by 11:59pm on May 19, 2025

Starter Files

Download lab11.zip. Inside the archive, you will find starter files for the questions in this lab.

Important
Your code for this lab should go in Grid.py.

Grid Class

In this lab, we’re going to build a simple grid class. Grids can be used to store values in a 2D space. We will build different tools to construct and work with grids.

Grid(width, height) - constructs new grid. Initially all locations are None
Grid.width, Grid.height - width/height properties
Grid.get(x, y) - returns contents at (x, y) (error if (x, y) out of bounds)
Grid.set(x, y, val) - sets value into the grid at (x, y) (error if (x, y) out of bounds)

Q1: Initializing

First, we will implement the Grid class constructor. This constructor takes two arguments:

An integer as the width of the grid
An integer as the height of the grid

Use these to create a list of length height and each element will be a list of length width. Each element of the inside lists should be initialized as None. Each Grid instance will keep track of these three values with instance attributes called width, height and array.

Hint
List comprehension could be helpful for creating our array.

def __init__(self, width, height):
    """
    Create grid `array` width by height. Create a Grid object with
    a width, height, and array. Initially all locations hold None.
    >>> grid = Grid(2, 2)
    >>> grid.array
    [[None, None], [None, None]]
    """

The array should be constructed so it looks something like this, but with the correct specified dimensions for width and height of the outer and inner lists. This example shows a representation of a grid object Grid(2, 2):

[[None, None],
[None, None]]

Testing

We’re writing a class that is designed to be imported into other programs. To test your class as you are writing it, you should create a separate python file to write code to test your Grid class. Create that file now and add an import line to the top of it:

from Grid import Grid

Then try creating a new grid object and accessing the height and width attributes. If you don’t get any errors, you are good to go. Otherwise, work with your lab partners and TAs to figure out what is not working. Now you are ready to add functionality to the class.

Q2: `get()` and `set()`

Write out a get() method and a set() method with the function signatures given below. Get should take in an $x$ and $y$ coordinate and return the value at that cell in the grid. Set will use an $x$ and $y$ coordinate and set that cell to val. Set returns None.

def get(self, x, y):
    """
    Gets the value stored value at (x, y).
    (x, y) should be in bounds.
    >>> grid = Grid(2, 2)
    >>> grid.array = [[1, 2], [4, 5]]
    >>> grid.get(0, 1)
    4
    >>> grid.get(1, 0)
    2
    """


def set(self, x, y, val):
    """
    Sets a new value into the grid at (x, y).
    (x, y) should be in bounds.
    >>> grid = Grid(2, 2)
    >>> grid.set(1, 1, "Milk")
    >>> grid.set(1, 0, "Dud")
    >>> grid.array
    [[None, 'Dud'], [None, 'Milk']]
    """

Both of these methods should validate that the $x$ and $y$ coordinates are valid and within the width and height specified for the grid. If they are invalid, the methods should raise an IndexError. Think back to Lab 6 for how you should do this.

Hint
Since you’ll need it for both get() and set(), you should write an in_bounds() method that checks to see if the $x$ and $y$ coordinates are valid. You’ll also need that check in other parts of the Grid class later on.

Q3: `str()` and `repr()`

Now we’ll create the __str__() and __repr__() methods.

def __str__(self):


def __repr__(self):

The __str__() method should return a “human-readable” string that represents the class. For our implementation, we’ll have __str__() return the following:

Grid(<width>, <height>, first = <first element>)

Where <width> and <height> are the values stored in the instance variables and <first value> is the first value (index 0,0) in the data array.

The __repr__() function is supposed to return a string that if we pasted it into a Python script or called Python’s eval() function, would recreate the object. We don’t yet have everything in this class we need to do that. You’ll add that part of the class in Homework 3. For now, just have __repr__() return the same value as the __str__() method.

What's the difference?
If you’re having trouble knowing the difference between these here’s an analogy. Consider the difference between drawing a flower and writing out the word ‘flower’. Drawing a flower is like the __repr__() function, because the drawing will look like the object. Writing out the word ‘flower’ is like __str__(), because it’s a text description, not a visual representation.

Q4: `eq()`

The __eq__() dunder method is what python calls when you use the == operator to compare the instances of class. Write a function that can compare two Grid’s and decide if the arrays are the same size and contain the same values.

The function signature for this method is:

def __eq__(self, other):

where the variable other is the Grid object that we are comparing with.

This method should make two checks:

First, it should check to see if other is another Grid object (use Python’s isinstance() function). If not, it should return False.
Second, return the expression self.array == other.array. This will check both:
- That self and other have the same dimensions
- That each space in self and other match
Hint
You don’t need to manually compare the lists, == will do it for you.

Submit

Submit the Grid.py file on Canvas to Gradescope in the window on the assignment page.

Lab 11 - Grids