rpn

Is there a better way to handle unary "-" in converting a infix expression to a postfix one? The obvious one would be prefix every unary "-" with a 0. Does anyone know better implementation? Thanks! The way I did this years ago was invent a new operator for my postfix expression. So when I encountered a unary minus in the infix, I'd convert it to # . So my postfix for a + -b became ab#+ . And, of course, my evaluator had to know that # only popped one operand. Kind of depends on how you're using the postfix expression once it's built. If you want to display it then your special # operator

Here is a Python postfix notation interpreter which utilizes a stack to evaluate the expressions. Is it possible to make this function more efficient and accurate? #!/usr/bin/env python import operator import doctest class Stack: """A stack is a collection, meaning that it is a data structure that contains multiple elements. """ def __init__(self): """Initialize a new empty stack.""" self.items = [] def push(self, item): """Add a new item to the stack.""" self.items.append(item) def pop(self): """Remove and return an item from the stack. The item that is returned is always the last one that