As with last week, the assignment is to bring together the lsystem and turtle interpreter classes to make a scene that consists of fractal shapes and trees. Your top-level program will import both the lsystem and interpreter modules. Unlike last week, however, your scene.py may not import the turtle module or make any calls to turtle commands directly. If you want to draw something, you have to pass a string to the interpreter drawString method. There will be no exceptions to that rule. (Note that you may attach arbitrary meaning to any character not used by an L-system grammar.)


  1. We want to be able to change the color of elements in an Lsystem without affecting the color of other elements. We would also like to avoid setting colors, widths, or other turtle drawing features by adding new parameters to drawString. Instead, modify your drawString method so that it handles five additional characters in the strings.

    • '<' - the left angle bracket should push the current turtle color onto a color stack. You'll need to create a separate colorstack variable similar to the one used for position and heading. You can use the function turtle.color() to get the turtle's current color. Note that this function returns a tuple of colors. You should append just the first element of the tuple onto the color stack.

      colorstack.append( turtle.color()[0] )

    • '>' - the right angle bracket should pop the current turtle color off the color stack and set the turtle's color to that value.
    • 'g' - set the turtle's color to green (e.g. (0.15, 0.5, 0.2) ).
    • 'y' - set the turtle's color to light yellow ( e.g. (0.8, 0.8, 0.3) ).
    • 'r' - set the turtle's color to red ( e.g. (0.7, 0.2, 0.3) ).

    Be sure to use the turtle.color() and turtle.width() methods properly. They are turtle functions, and the new color or new width needs to be an argument to the function.

    Once you have made the modifications to drawString, try running systemFL using the classtest.py test function from the lab. You can also use the test function single.py to draw just a single tree.

  2. Create a file arrangement.py. Have the file import lsystem and turtle_interpreter (the new versions). Write a function that makes an arrangement of trees or flowers. The scene should include some multi-rule L-systems with leaves or other ornaments that make use of the color store/restore. You can use the symbol L to indicate a leaf, which could be drawn as a semicircle or a circle or a line. The following are variations with leaves and flowers, all defined by strings (no special characters except L). Try to include L-system trees with different numbers of iterations. (Note that at least two of the L-systems you use must have at least 2 rules.)
    systemCL systemDL systemEL systemFL systemGL

    This is required image 1.

    Please indicate either in your write-up or in your code which L-systems you use. If you happen to use command line arguments to specify filenames and don't tell us which systems you used, then we can't run your code to reproduce your image. So either hard-code which L-systems you use or indicate which ones you used to make the pictures in your report.

  3. Make two new L-systems. They can be variations on one of the ones provided, an variation on an L-system from the ABOP book, or one you create on your own. The L-systems of interest are given in the ABOP book chapter 1, pages 10, 11, and 25.

    If you use a variation, include both the original and your variant in your writeup. (The difference does not have to be large.)

    In the file growth.py, create a scene function that makes an image using your L-systems after 2, 3, and 4 iterations. Note, if using a different pattern of iterations is more interesting (e.g. 4, 5, 6 or 2, 4, 6) you are free to use a different set of three iteration values. Indicate what you used in your writeup.

    This is required image 2.

    Please indicate either in your write-up or in your code which L-systems you used (and include the txt files for your new L-systems with your code when you turn it in!).

Example Extensions


Make a new wiki page for your assignment. Put the label cs151s18project8 on the page. Each of you needs to make your own writeup.

In addition to making the wiki page writeup, put the python files you wrote on the Courses server in your private directory in a folder named project8.

Colby Wiki

In general, your writeup should follow the outline below.

© 2018 Caitrin Eaton.