Question

Python Assignment: Write a program that uses stacks to solve postfix equations.Read the below in a strings, character by character, into a stack and solve them. 3 2 + 4 * 5 1 - /

Answer 1

Hey here is answer to your question.

class Stack:
def __init__(self):
self.items = []

def push(self, item):
self.items.append(item)
def pop(self):
return self.items.pop()
def is_empty(self):
return (self.items == [])
def cal_postfix(s,string):
#loop over expression
for i in string:
#if its a digit then push to stack
if i.isdigit():
s.push(i)
           # if its not a digit then pop last 2 values and
           # eval the expression and push that to stack
else:
val1 = s.pop()
val2 = s.pop()
s.push(str(eval(val2 + i + val1)))
       # do that for whole string at last pop final value
return s.pop()
exp = "32+4*51-/"
# make a stack
s = Stack()

# call function with args as stack and expression
print(cal_postfix(s,exp))

In case of any doubt please comment. Happy Learning :)