On Apr 3, 10:57 am, [EMAIL PROTECTED] wrote:
> Hi! Im new to Python and doing exercise found from internet. It is
> supposed to evaluate expression given with postfix operator using
> Stack() class.
>
> class Stack:
> def __init__(self):
> self.items = []
>
> def push(self, item):
> self.items.append(item)
>
> def pop(self):
> return self.items.pop()
>
> def isEmpty(self):
> return (self.items == [])
>
> def evaluatePostfix(expr):
> import re
> tokenList = re.split(" ([^0-9])", expr)
> stack = Stack()
> for token in tokenList:
> if token == '' or token == ' ':
> continue
> if token == '+':
> sum = stack.pop() + stack.pop()
> stack.push(sum)
> elif token == '*':
> product = stack.pop() * stack.pop()
> stack.push(product)
> else:
> stack.push(int(token))
> return stack.pop()
>
> print evaluatePostfix("56 47 + 2 *")
>
> Errormsg:
> Traceback (most recent call last):
> File "C:\*\postfix1.py", line 31, in <module>
> print evaluatePostfix("56 47 + 2 *")
> File "C:\*\postfix1.py", line 28, in evaluatePostfix
> stack.push(int(token))
> ValueError: invalid literal for int() with base 10: '56 47'
>
> How can I avoid the error and get desired result?
I don't know why you're using the "re" module. For this, I would skip
it. Change your code so that it looks like this:
def evaluatePostfix(expr):
tokenList = expr.split(" ")
stack = Stack()
for token in tokenList:
if token == '' or token == ' ':
continue
if token == '+':
sum = stack.pop() + stack.pop()
stack.push(sum)
elif token == '*':
product = stack.pop() * stack.pop()
stack.push(product)
else:
stack.push(int(token))
return stack.pop()
# this worked for me. There may be something wrong with the "re" code
in your example, but I don't know enough about that to help in that
area.
Mike
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