Due: , 11:59 pm
The purpose of this lab is to give you practice in creating your own classes. In particular, we will convert both the lsystem and the turtle interpreter modules into classes. Ultimately, this will make it easier to build a more complex system.
If you have not already done so, take a look at the book 'The Algorithmic Beauty of Plants', which is the basis for this series of lab exercises. You can download the entire book from the algorithmic botany site
The other piece we'll be implementing this week is handling multi-rule L-systems. Adding this capability will enable you to draw more complex L-system structures.
Most of the exercises in lab will involve building up an L-system class. This week it will be important for you to use the method names provided. The next several labs will expect the L-system and TurtleInterpreter classes to have certain methods with particular names.
Then we define the __init__() method, which is executed when a Lsystem object is created. The init method should set up the fields of a class and give them reasonable initial values. Init methods often take optional arguments. You can make an argument optional by assigning a value to it in the argument list of the method declaration. For example, the following function has two arguments, the second of which is optional with a default value of 5.
def boo( a, b = 5 ): print(a, " ", b)
The Lsystem init method should have two arguments: self, and an optional filename. If the method receives a filename, it should read Lsystem information from the file by calling the read method of self (which you'll create below), passing the filename as the argument.
def __init__(self, filename=None):
The Lsystem init should create two fields: base and rules. The field base should be initialized to the empty string. The field rules should be initialized to an empty list. To create a field of a class, put the prefix self. in front of the name of the field and assign something to it. The line of code below creates the field base and assigns it the empty string.
self.base = ''
Here is the template for the init method
def __init__( self, filename = None ): # assign to the field base, the empty string # assign to the field rules, the empty list # if the filename variable is not equal to None # call the read method of self with filename as the argument
You can use the following template
def read( self, filename ): # assign to a variable (e.g. fp) the file object created with filename in read mode # assign to a variable (e.g. lines) the list of lines in the file # call the close method of the file # for each element in the lines list # assign to a variable (e.g. words) the result of calling the split() method on the loop variable # if the first item in words is equal to the string 'base' # call the setBase method of self with the new base string # else if the first item in words is equal to the string 'rule' # call the addRule method of self with the new rule (the slice of words from index 1
Once you are done with all of the above steps, download and run this test function. It should nicely print out a single rule L-system read from a file and then print out a second L-system created in the test program. Running the program with systemA1.txt as the command line argument, you should get the output below.
Case 1 systemA1.txt F-F-F-F F -> F-FF--F-F Case 2 F--F--F F -> F+F--F+F
def replace(self, istring): # assign to a local variable (e.g. tstring) the empty string # for each character c in the input string (istring) # set a local variable (e.g. found) to False # for each rule in the rules field of self # if the symbol in the rule is equal to the character in c # add to tstring the replacement from the rule # set found to True # break # if not found # add to tstring the character c # return tstring
def buildString(self, iterations): # assign to a local variable (e.g. nstring) the base field of self # for the number of iterations # assign to nstring the result of calling the replace method of self with nstring as the argument # return nstring
python lsystem.py systemA1.txt
Be sure to put an import sys at the top of your file. The test code should print out the lsys object (which will look odd, the base string, and the first rule. In addition, it will print out the result of running 2 iterations of replacement on the base string.
def main(argv): if len(argv) < 2: print('Usage: lsystem.py <filename>') exit() filename = argv iterations = 2 lsys = Lsystem() lsys.read( filename ) print( lsys ) print( lsys.getBase() ) for i in range( lsys.numRules() ): rule = lsys.getRule(i) print( rule + ' -> ' + rule ) lstr = lsys.buildString( iterations ) print( lstr ) return if __name__ == "__main__": main(sys.argv)
You can download and run the file on any of the following examples. Systems C through G require multiple rules.
def __init__(self, dx = 800, dy = 800): # call turtle.setup with dx and dy as the arguments # set the turtle tracer to false (optional)
def drawString(self, dstring, distance, angle):
Add the following methods to your turtle interpreter class.
When you are done with the lab exercises, you may start on the rest of the project.
© 2018 Caitrin Eaton.