CS 240

Homework 1: Basic Python

Objectives

The goal of this homework is to verify mastery of the basic features of the Python programming language including functions, variables, loops, strings, and lists.

This lab is based on work done in previous labs: shapes and strings.

Part 1: Checkerboard

Building on the code that you wrote in the first lab, write a new turtle graphics function with the following signature:

        checkerboard(x, y, rows, columns, size)

This function should create a rows x columns grid of colored squares. The lower-left corner of the checkerboard will be at position (x,y). The size parameter indicates the width of the individual squares.

Alternating squares should be filled with blue in a checkerboard pattern, and the lower-left square should be filled in. You will need to look through the documentation for the begin_fill() and end_fill() functions. Here is an example of what a 3x8 checkerboard should look like:

Part 2: Polygon File Drawing

Write a function with the following signature:

        draw_polygon_file(fname)

This function should take a file name as a parameter, and draw the polygons stored in that file. You should re-use your polygon function from the shapes lab. The file format consists of a series of polygon specifications with four integers per polygon and one polygon per line. The line format for one polygon is:

        x_pos y_pos sides size

Each integer is separated by a space. Here is an example of two lines from such a file:

        0 0 3 50
        50 100 4 20

The above lines would encode a 50-pixel wide triangle at position (0, 0), and a 20-pixel wide square at position (50, 100).

You will need to use some very basic Python file I/O for this part, and for this you should reference Section 1.6 in your textbook as well as the documentation. I recommend using the readlines() function to read all lines into a list after you have open()'ed the file. That will simplify the process of splitting the strings and using the parameters to draw polygons.

Here are some sample files you can test with:

• polygons-simple.txt
• polygons-pic01.txt
• polygons-pic02.txt

Part 3: String Formatting

Write a function with the following signature:

        format_str(description, values)

This function should return a reformatted version of description, where special identifier words like "$3" have been replaced by the specified element from values. The special identifiers should always be a single word (no spaces) composed of a single dollar sign ("$") followed by the zero-based index of the desired value.

Your function should work regardless of whether the values are strings, integers, or floating-point numbers. Your function should also check to make sure the given index is within the bounds of the given list. If it is not, your function should insert the text "ERROR".

Here are some examples:

        format_str("Hello $0", ["World"])
            # result: "Hello World"

        format_str("The sum of $0 and $1 is $2", [3,5,8])
            # result: "The sum of 3 and 5 is 8"

        format_str("The name is $1 -- $0 $1", ["James", "Bond"])
            # result: "The name is Bond -- James Bond"

        format_str("Names: $0 $1 $2 $3", ["Mike", "Nathan"])
            # result: "Names: Mike Nathan ERROR ERROR"

To extract the index number from a special identifier, you may wish to use a technique called slicing. You can find information about it in the Python string documentation.

    This submission compiles with the JMU Honor Code. All code was written by
    the submitter, and no unauthorized assistance was used while completing this
    assignment.