[Tutor] OOP design (w/ example :-)

[Timothy Wilson]

Hey everyone,

I'm back working on a little Python program, trying to scratch a specific
itch that I keep having with my students at school. Specifically, I often
want to put my students in small groups to work on class work, labs, or
whatever we're working on that day. It's too time consuming to go through a
big process every day and I want to rearrange the groups often. I thought a
small computer program would be just the ticket.

To keep things simple for now, I'm storing the students in a simple text
file with last name, first name, and gender. (At some point I'd like to have
the option of mixing gender in the groups.) Here's a sample file:

van Rossum,Guido,M
Boop,Betty,F
Gauld,Alan,M
Flintstone,Wilma,F
Rubble,Betty,F
Yoo,Danny,M
Wilson,Tim,M
Crawford,Cindy,F
Van Laningham,Ivan,M
Lutz,Mark,M
Ascher,David,M
Watters,Aaron,M

I'd like to try a OOP approach, but one of the things I struggle with is the
initial design stage. I've asked about this before and I've done some
reading, but I still haven't found a way of thinking about problems like
this that make a lot of sense to me.

My program, it would seem, would logically have classes the correspond to
individual students, groups, and perhaps the class as a whole. Here's what
I've come up with so far:

class Student:
	def __init__(self, ln, fn, gender):
		self.ln = ln
		self.fn = fn
		self.gender = gender
		
class Group:
	def __init__(self, studentList):
		self.studentList = studentList
	def display(studentList):
		pass

class Roster:
	def __init__(self):
		pass
	def loadFile(self, filename):
		import string
		classList = []
		f = open(filename, 'r')
		while 1:
			try:
				record = f.readline()
				student = string.split(record, ',')
				ln = student[0]
				fn = student[1]
				gender = student[2][:1]
				classList.append(Student(ln, fn, gender))
			except EOFError:
				break
		return classList

Note, this code doesn't currently work. I get this:

Python 1.5.2 (#0, Apr  3 2000, 14:46:48)  [GCC 2.95.2 20000313 (Debian
GNU/Linux)] on linux2
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>> import group
>>> roster = group.Roster()
>>> classList = roster.loadFile('class.dat')
Traceback (innermost last):
  File "<stdin>", line 1, in ?
  File "group.py", line 29, in loadFile
    fn = student[1]
IndexError: list index out of range
>>>

I'd love to hear some advice from others on the list. What design advice can
you give? Any other suggestions?

-Tim

--
Tim Wilson      | Visit Sibley online:         | Check out:
Henry Sibley HS | http://www.isd197.k12.mn.us/ | http://www.zope.org/
W. St. Paul, MN |                              | http://slashdot.org/
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