Python 3

(use Stack to evaluate the postfix expression as shown in lecture slides)

1.Write a function that accepts a valid postfix expression and evaluates it.

CODE:

# Stack.py class Stack: #------------------------------------------------------------ def __init__(self): '''post: creates an empty LIFO stack''' self.items = [] #------------------------------------------------------------ def push(self, item): '''post: places x on top of the stack''' self.items.append(item) #------------------------------------------------------------ def pop(self): '''post: removes and returns the top element of the stack''' return self.items.pop() #------------------------------------------------------------ def top(self): '''post: returns the top element of the stack without removing it''' return self.items[-1] #------------------------------------------------------------ def size(self): '''post: returns the number of elements in the stack''' return len(self.items)