CS 151: Project 9

Title image Project 9
Spring 2020

Project 9: Unique Trees and Mosaics

The project this week is to continue to make shape classes, making use of inheritance, starting with a tree class.


  1. Make a Tree class

    The first task is to make a Tree shape class, similar to the Square and Triangle classes. The difference between a Tree and a Square, though, is that the Tree generates its string dynamically using an L-system. The string for a Square is always the same, so it can set the string field once and then use the parent Shape class' draw method. However, every time the Tree class draws a tree, it should first build a new string using an L-system. Then it can call the Shape class draw method.

    The Tree class needs to use an L-system to generate the string to draw, so a Tree object must contain a field that holds an L-system object.

    Because a Tree is a Shape, it should be a child of the Shape class. That lets it use the parent methods for setting color, distance, and angle, among other things.

    To make the Tree class, start by creating a file called tree.py. Import the lsystem and shape modules. The Tree class should be derived from the Shape class, but it will need to override some of the methods because of the special nature of a Tree: it needs more fields than a simple Shape, and it has to dynamically create the string it will draw using an L-system.

    The methods you'll need to override or create for the Tree class include:

    • def __init__(self, distance=5, angle=22.5, color=(0.5, 0.4, 0.3), iterations=3, filename=None):

      The init method should call the parent (Shape) init method with self, distance, angle, and color. It should assign the iterations value to an iterations field of the object (self). Finally, it should create an Lsystem object (passing in the filename) and assign it to an lsystem field of self.

    • def setIterations(self, N):

      Given a new number of iterations in N, assign it to the iterations field of the object.

    • def read(self, filename):

      The read(self, filename) method should call the lsystem object's read method with the specified filename. Use the Lsystem object you created and stored in the lsystem field to call the read method.

    • draw(self, xpos, ypos, scale=1.0, orientation=90):

      Override the draw method--but keep the same parameter list. Use the draw method use the Lsystem to build a string. Then assign the string to the string field of self and call the parent class (Shape) draw method. Note the suggested default orientation for this function to be 90 so the trees grow up.

    Once you've written the tree class, make a test method for the class and try it out. The test method should take in an Lsystem filename as a parameter, create a Tree object, and then use the Tree object's draw method to draw at least 3 trees in different locations. Use an L-system with multiple replacements for at least one rule (e.g. systemJ.txt and show the three trees are different.

    The output of your tree.py test method is required image 1.

  2. Create three more shape classes

    In shapes.py, create at least three classes--other than Square and Triangle--that are derived from the Shape class and define different shapes using strings. One of them should make a filled shape using curly brackets { and } to turn on and off the fill. Make a test function for your shapes.py file that generates an image that incorporates all of the shapes you created. The function should test all of the capabilities of the different shape classes.

    The output of your shapes.py test method is required image 2.

  3. Create a scene of a place outdoors where you like to be

    In a file named place.py, create a new scene representing a place outdoors that is meaningful to you. Give your scene a title in your report. Use your various shape classes and include at least one tree in the scene. Use only the Tree and shape classes from this assignment to create the scene, not your turtle code from prior assignments. Use the TurtleInterpreter only to call the hold method. Only the TurtleInterpreter class should execute turtle commands.

    The outdoor scene is required image 3.

  4. Create a grid of tiles

    Loosely inspired by MC Escher or Islamic Mosaics, create a grid of 20 tiles.

    In a file named mosaic.py, create a function tile(x, y, scale) that draws a set of shapes inside a square that is scale by scale in size with the lower left corner of the tile at location (x, y). If scale is 10, then the tile should be 10x10.

    Define a function mosaic(x, y, scale, Nx, Ny) that draws a 2D array of tiles Nx by Ny, where each tile is of size scale by scale, and the lower left corner of the mosaic is at (x, y). So if scale is 10, Nx is 3, and Ny is 4, the function should draw twelve 10x10 tiles in a grid three across and four down.

    Just like in the previous task, use only the Tree and shape classes from this assignment to create the scene, not your turtle code from prior assignments. Only the TurtleInterpreter class should execute turtle commands.

    An image of at least 20 tiles (5 x 4) in a non-square arrangement is required image 4.

Follow-up Questions

  1. What is inheritance?
  2. What does it mean for a child class to override a method?
  3. What is a class variable or class global variable?
  4. What is a field of an object?
  5. Which image or artwork did you choose as inspiration? Why?


Extensions are your opportunity to customize your project, learn something else of interest to you, and improve your grade. The following are some suggested extensions, but you are free to choose your own. Be sure to describe any extensions you complete in your report. Include pictures.

Submit your code

Turn in your code (all files ending with .py) by putting it the appropriate directory in the Courses server. You can access Courses through a browser at vpn.colby.edu. On the Courses server, you should have access to a directory called CS151, within that, a directory with your user name, and within that a directory named Private. Inside the Private directory there is a Projects directory with sub-directories for each week's project where you should submit your code. Please submit only code that you want to be graded.

When submitting your code, double check the following.

  1. Is your name at the top of each code file?
  2. Does every function have a comment or docstring specifying what it does?
  3. Is your handin project directory inside your Private folder on Courses?

Write Your Project Report

If you haven't already made a new page for this report on the wiki, then make one now (Log into the wiki, goto your Personal space by selecting "Personal Space" on the menu under the Person icon, then make the page using the "Create" button. Put the label cs151s20project9 in the label field on the bottom of the page. But give the page a meaningful title.

Your intended audience for your report is your peers not in the class. From week to week you can assume your audience has read your prior reports. Your goal should be to be able to use it to explain to friends what you accomplished in this project and to give them a sense of how you did it.

Your project report should contain the following elements. Please include a header for each section.