First Tkinter script: requesting comments

[Bart Kastermans]

I wrote a first script using Tkinter.  As I am new to its
use, I am only just feeling my way around.  I would very
much like comments on the design of the script (and in fact
any other comments on my code would also be very welcome).

I have it posted (with syntax coloring) at:

http://kasterma.wordpress.com/2010/05/21/first-experiments-with-tkinter/

But will also include it here for convenience.

Thanks for any help,

Best,
Bart

***********************

#!/usr/bin/env python
#
# Getting a list of students and grades displayed so that grades can
# be updated, and we poll these changes (so that in the future we can
# act on it).
#
# Bart Kastermans, www.bartk.nl

"""
Design of the window

      +-------------------------------------------------------------+
      |  root                                                       |
      |  +------------------------------------------------------+   |
      |  | title_frame                                          |   |
      |  |  +------------------------------+                    |   |
      |  |  | Label(title)                 |                    |   |
      |  |  |                              |                    |   |
      |  |  +------------------------------+                    |   |
      |  +------------------------------------------------------+   |
      |  +------------------------------------------------------+   |
      |  | exam_grades_frames                                   |   |
      |  |  +-------------------------------------------------+ |   |
      |  |  | Frame(ex)                                       | |   |
      |  |  | +--------------------+  +---------------------+ | |   |
      |  |  | | Entry(name)        |  | Entry(grade)        | | |   |
      |  |  | |                    |  |                     | | |   |
      |  |  | +--------------------+  +---------------------+ | |   |
      |  |  +-------------------------------------------------+ |   |
      |  |                                                      |   |
      |  +------------------------------------------------------+   |
      |                                                             |
      |                 +---------------------+                     |
      |                 | quit_button         |                     |
      |                 |                     |                     |
      |                 +---------------------+                     |
      +-------------------------------------------------------------+

"""



from Tkinter import *

# global info for this specific example

# four students
no_stud = 4
exam_grades = [1,2,3,4]
names = ["Ben", "Jim", "James", "Mel"]
# upper bound for name length
max_name_len = max (map (len, names))

# set up root window
root = Tk()
root.geometry ("400x400")

exam_grades_string = map (lambda x: StringVar (root,str (x)), exam_grades)

names_string = map (lambda x: StringVar (root, x), names)

def setup ():
    """ setup the window with the list of students.

    This is test-code to figure out what the app finally should look
    like.
    """

    # title frame, with title Grade Correction in it
    title_frame = Frame(root)
    title_frame.pack (fill=X)

    w = Label (title_frame, text = "Grade Correction", font = ("Helvetica", 25))
    w.pack (side=LEFT)

    # from to hold the list of grades
    exam_grades_frame = Frame (root)
    exam_grades_frame.pack (fill=BOTH)

    exam_label = Label (exam_grades_frame, text="EXAMS")
    exam_label.pack ()

    # set up the list of grades
    for i in range (0,no_stud):
        # a frame per student
        ex = Frame (exam_grades_frame)
        ex.pack ()
        # name on the left
        name = Entry (ex, textvariable=names_string[i], width=max_name_len+2)
        name.config (state=DISABLED)
        name.pack (side=LEFT)
        # grade next to it
        grade = Entry (ex, textvariable=exam_grades_string [i], width=4)
        grade.pack (side=LEFT)

    # button to quit the application
    qb = Button (root)
    qb ['text'] = "quit"
    qb ['command'] = root.quit
    qb.pack ()


def to_int (st):
    """ helper function to convert strings to integers.

    Empty string represents 0.
    """
    if len (st) == 0:
        return 0
    else:
        return int (st)

def get_curr_grades ():
    """ extract the grades from exam_grades_string.

    exam_grades_string consists of StringVar that get updated when the
    fields are updated in the GUI.
    """
    grades = []
    for i in range (0, no_stud):
        grades.append (exam_grades_string [i].get())
    return grades

# get the current grades
curr_grades = map (to_int, get_curr_grades ())

def poll_exams ():
    """ function that keeps polling the current grades, looking for changes"""
    global curr_grades
    new_grades = map (to_int, get_curr_grades ())
    if new_grades != curr_grades:
        print new_grades
        curr_grades = new_grades
    root.after( 250, poll_exams)

# window setup
setup ()

# start the polling
poll_exams ()

# start the eventloop
root.mainloop ()

# do cleanup
root.destroy ()
sys.exit ()