Due: Tuesday, April 11, 2017, 11:59 pm

Better Trees

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 turtle_interpreter modules. Unlike last week, however, your main programs (arrangement.py and growth.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. Modify your drawString method so that it supports five additional characters in the strings. Don't forget to update the docstring of drawString to include the new characters

    • '<' - 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 (e.g. 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) ).

    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.

    At least two of the L-systems you use must have at least 2 rules. Like last week, please hard-code the filenames for the L-systems into your code, so that we can run your program without needing command line arguments.

    systemCL systemDL systemEL systemFL systemGL

    This is required image 1.

  3. Make two new L-systems. They can be variations on one of the ones provided, 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) you are free to use a different set of three iteration values. Indicate what you used in your writeup.

    Again, please hard-code the filenames for the L-systems into your code, rather than rely on command-line arguments. Also, be sure to put a copy of your new L-system's text file on the Courses server when you turn in your code.

    This is required image 2.


Write-up and Hand-in

Turn in your code by putting it into your private hand-in directory on the Courses server. All files should be organized in a folder titled "Project 8" and you should include only those files necessary to run the program. We will grade all files turned in, so please do not turn in old, non-working, versions of files.

Make a new wiki page for your assignment. Put the label cs151s17project8 in the label field on the bottom of the page. But give the page a meaningful title (e.g. Ying's Project 8).

In general, your intended audience for your write-up is your peers not in the class. 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. Follow the outline below.

To check whether you've made your images and their text clear, you may ask yourself the following questions:

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