OK I pretty new to python but I'm pretty sure this should work. everything is defined, only posted whats causing the problem. *expression* is a Reverse Polish Notation for a calculator (ex 1 2 +) and has already been parsed at this point into single array elements. All I get after running is a SERVER ERROR.

Code:

stack = []
i = 0
j = 0
for i in range(len(expression))
if len(expression) <= 2
print "Invalid Expression: Not enough elements"
break
if expression[i] == '+' || expression[i] == '-' || expression[i] == '*'
if i == 0 || i == 1
print "Invalid Expression: Operator out of place!"
break
if expression[i] == '+'
stack[j-2] = stack[j-2] + stack[j-1]
j = j - 1
stack[j] = ""
if expression[i] == '-'
stack[j-2] = stack[j-2] - stack[j-1]
j = j - 1
stack[j] = ""
if expression[i] == '*'
stack[j-2] = stack[j-2] * stack[j-1]
j = j - 1
stack[j] = ""
else
stack[j] = int(expression[i])
j = j + 1
print stack[0]