You should check if the stack is empty before you access it:
def popNum(num):
if len(stackA) > 0 and num == stackA[-1]:
stackA.pop()
#etc
--Michael
--
Michael Langford
Phone: 404-386-0495
Consulting: http://www.TierOneDesign.com/
Entertaining: http://www.ThisIsYourCruiseDirectorSpeaking.com
On 9/19/07, bhaaluu <[EMAIL PROTECTED]> wrote:
>
> Greetings,
> I'm working with Python 2.4.3 on the GNU/Linux platform.
> I'm currently playing with functions and stacks, and am
> using the "Towers of Hanoi" as a test game to play with.
> Note: This game is not a recursive programming exercise,
> it is meant to be solved by the player, manually.
>
> The game asks for a number to move, and a stack to move it to.
> The game starts out in this state:
> =========================
> A [5, 4, 3, 2, 1] False
> B [] True
> C [] True
> =========================
> Enter number and stack to move it to: 1b
>
> It seems to work fine with my test moves:
>
> 1b 2c 1c 3b 1a 2b 1b 1b 4c 1c 2a 1a 3c 1b 2c 1c 5b
> Which brings the game to this state:
>
> Enter number and stack to move it to: 5b
> 5 B
> A [] True
> B [5] False
> C [4, 3, 2, 1] False
> =========================
>
> Then, in the second round of test moves, it bombs on the first move:
>
> Enter number and stack to move it to: 1b
> 1 B
> Traceback (most recent call last):
> File "funcStack.py", line 73, in ?
> moveNum(num,abc)
> File "funcStack.py", line 52, in moveNum
> popNum(num)
> File "funcStack.py", line 32, in popNum
> if num == stackA[-1]:
> IndexError: list index out of range
>
> The second round of test moves are:
> 1b 2a 1a 3b 1c 2b 1b 4a 1a 2c 1c 3a 1b 2a 1a 5c
> The third round of test moves are:
> 1b 2c 1c 3b 1a 2b 1b 1b 4c 1c 2a 1a 3c 1b 2c 1c
> Which should bring the game to this state:
> =========================
> C [] True
> B [] True
> A [5, 4, 3, 2, 1] False
> =========================
>
> Here is my Python source code:
> # funcStacks.py
> # passing parameters, returning values, pushing and popping
> # 2007-09-19
> # b h a a l u u at g m a i l dot c o m
> ######################################
> """
> Pseudocode
> 1. Get the number to move and the column to move it to: 1b, 2c, etc.
> 2. Find the column the number is in: A, B, or C
> 3. Is it the last number (ie. can it be popped?) num == stackA[-1]
> 4. If the number can be popped, pop it! stackA.pop()
> 5. Else, number is buried: return an error and try again.
> 6. Determine if the number can be legally moved to the column requested.
> 7. If the column is empty, move the number: stackB.append(num)
> 8. If the column has a number, is it larger? stackB.append(num)
> 9. Else if number in column is smaller, return an error and try again.
> 10. Loop.
> """
> num = 0
> abc = ""
> EMPTY = []
> stackA = []
> stackB = []
> stackC = []
>
> def isEmpty(stack):
> if stack == EMPTY:
> return True
> else:
> return False
>
> def popNum(num):
> if num == stackA[-1]:
> stackA.pop()
> elif num == stackB[-1]:
> stackB.pop()
> elif num == stackC[-1]:
> stackC.pop()
> else:
> return "Error: number not available."
>
> def pushNum(num,abc):
> if abc == 'C':
> stackC.append(num)
> elif abc == 'B':
> stackB.append(num)
> elif abc == 'A':
> stackA.append(num)
> else:
> return "Move not allowed, try again."
>
> def moveNum(num,abc):
> popNum(num)
> pushNum(num,abc)
> return stack_status()
>
> def stack_status():
> print "A",stackA, isEmpty(stackA)
> print "B",stackB, isEmpty(stackB)
> print "C",stackC, isEmpty(stackC)
>
> # main
> print '='*25
> stackA=[5,4,3,2,1]
> stack_status()
> print '='*25
>
> myMove = raw_input('Enter number and stack to move it to: ')
> while myMove != 'Q':
> num = int(myMove[0])
> abc = str.upper(myMove[1])
> print num, abc
> moveNum(num,abc)
> print '='*25
> myMove = raw_input('Enter number and stack to move it to: ')
>
> Remember, I'm learning Python. I haven't studied OOP yet, so
> suggestions to make a class out of it won't help me much. =)
> --
> bhaaluu at gmail dot com
> _______________________________________________
> Tutor maillist - Tutor@python.org
> http://mail.python.org/mailman/listinfo/tutor
>
_______________________________________________
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
