#!/usr/bin/env python

'''

$Id$

queue_lab.py -- simulate queue data structures using lists

NOTE: as of the time of publication, there is a bug in JPython1.1

that does not recognize arguments for the list pop() method:

TypeError: pop(): expected 0 args; got 1

Exercises:

13-9) create a Queue class

13-10) create a class similar to arrays in Perl which have

both queue- and stack-like qualities and features

'''

# create our data structure

queue = []

#

# enQ() -- add string to end of queue

#

def enQ():

queue.append(raw_input('Enter new queue element: '))

#

# deQ() -- remove string from front of queue

#

def deQ():

if len(queue) == 0:

print 'Cannot dequeue from empty queue!'

else:

print 'Removed [', queue.pop(0), ']'

#

# viewQ() -- display queue contents

#

def viewQ():

print str(queue)

#

# showmenu() -- interactive portion of application

# displays menu to prompt user and takes

# action based on user response

#

def showmenu():

prompt = """

(E)nqueue

(D)equeue

(V)iew

(Q)uit

Enter choice: """

# loop until user quits

done = 0

while not done:

# loop until user choses valid option

chosen = 0

while not chosen:

# if user hits ^C or ^D (EOF),

# pretend they typed 'q' to quit

try:

choice = raw_input(prompt)[0]

except (IndexError, EOFError, KeyboardInterrupt):

choice = 'q'

print '\nYou picked: [%s]' % choice

# validate option chosen

if choice not in 'devq':

print 'invalid option, try again'

else:

chosen = 1

# take appropriate action

if choice == 'q':

done = 1

if choice == 'e':

enQ()

if choice == 'd':

deQ()

if choice == 'v':

viewQ()

# run showmenu() as the application

if __name__ == '__main__':

showmenu()