[Tutor] generators and classes

[Marilyn Davis]

Hello again,

I wrote this little program to demonstrate a generator:

#! /usr/bin/python2.2
'''Function to generate random numbers without repetition.
Demonstrates generators and the 'yield' keyword.'''

from __future__ import generators
import random

def unique(bot, over_top):
    '''Generator to deliver randomly chosen values from bot
    to over_top - 1, delivering each value once only.'''
    taken = [0] * (over_top - bot)
    while (1):
        give = random.randrange(bot, over_top) 
        if not taken[give - bot]:
            taken[give - bot] = 1
            yield give

def list_unique(bot, over_top):
    '''Returns a list of the generated numbers'''
    gen = unique(bot, over_top)
    return [gen.next() for i in range(bot, over_top)]

if __name__ == '__main__':
    print '(0,5) = ', list_unique(0,5)
    print '(10,21) = ', list_unique(10,21)

#############################
# OUTPUT:
# bash-2.05a$ ./unique.py
# (0,5) =  [2, 3, 1, 0, 4]
# (10,21) =  [17, 10, 18, 20, 19, 15, 11, 13, 12, 16, 14]
# bash-2.05a$     

-----

But now that I'm preparing to teach OO, I want to do the class
equivalent, which turns out like this:

#! /usr/bin/env python2.2

import random

class NumberHat:
    '''Generator to deliver randomly chosen values from bot
to over_top - 1, delivering each value once only.'''
    def __init__(self, bot, over_top):
        self.bot = bot
        self.over_top = over_top
        self.taken = [0] * (over_top - bot)

    def take(self):
        while 1:
            give = random.randrange(self.bot, self.over_top) 
            if not self.taken[give - self.bot]:
                self.taken[give - self.bot] = 1
                return give

if __name__ == '__main__':
    hat = NumberHat(0,10)
    for i in range(10):
        print hat.take()
            
############################################################
# OUTPUT:
# bash-2.05a$ ./numberhat.py
# 1
# 5
# 6
# 9
# 3
# 7
# 0
# 8
# 2
# 4
# bash-2.05a$ 

---

But there's no generator in it.  Is this natural?  Or is there
some other thought I should be thinking?

Thank you again and again.

Marilyn