Python program Can someone help me please to write a Python program that support

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Python program

Can someone help me please to write a Python program that support a processing of arithmetic expressions in postfix notation.
Expressions in postfix notation contain the operands on which the operation is performed followed by an operator. For example, 3 4 + is equal to 3 + 4 in the infix notation. float numbers and the following operators: + - * / ^ (all float operators) should be supported

There are a variety of ways to implement the postfix notation interpreter. One way is to use stacks. Another would be to use a tree.

The interpreter should accept strings of operators and operands seperated by spaces (no parenthesis) from standard input, and print the final result or output an error if the input is invalid. Each line will be a separate expression. EOF is the signal to quit.

Here is some sample input:

2.3 4 6.5 * + 3 5 + *
3 4 / 5 6 * - 2 -
3 2 - 2.8 +

Algorithm for evaluating postfix expressions

Start at the first token. For each token:

If it is an operand, push it on the stack.
Else if it is an operator, then

        pop top value into y

         if operator is binary:

              pop top value into x

             result <- x (oper) y

        else

            result <- (oper) y

       push result onto stack

       fi
fi

Continue until you've reached the end of the expression. There should be exactly one element in the stack; the result of the expression.

If you hit an operator and don't have sufficient operands on the stack (you'd better check) the expression is invalid. If you run out of tokens, and there's more than 1 operand on the stack, the input was invalid.

Simplle output

The result nedds to be printede (and just the result) of each expression, one per line, as each line is evaluated. No other output. So, interactively, this would be used in a very natural way.

If the expression is invalid you will print -E- .

Thaks!

someone helped me with this code but it is not working

import Stack

def postfixEval(postfixExpr):
operandStack = Stack()
tokenList = postfixExpr.split()

for token in tokenList:
if token in "0123456789":
operandStack.push(int(token))
else:
operand2 = operandStack.pop()
operand1 = operandStack.pop()
result = doMath(token,operand1,operand2)
operandStack.push(result)
return operandStack.pop()

def doMath(op, op1, op2):
if op == "*":
return op1 * op2
elif op == "/":
return op1 / op2
elif op == "+":
return op1 + op2
else:
return op1 - op2

print(postfixEval('3 4 / 5 6 * - 2 -'))

Explanation / Answer

Postfix Evalution:
it follws rules
1.The operators are written after their operands ex : (A+B) ===> AB+
2.Order of evaluation of the operators from left to right and the brackets cannot be used to change this order: 3 4 / 5 6 * - 2 -

For your code not handling error codes. below is the code with error handling.
please add this code
for token in tokenList:
if token in "0123456789": # Token numbers
   operandStack.push(int(token))
elif token == '-': # any operator you canuse
       if not operandStack.is_empty():
       x = operandStack.pop()
       else:
       print(" An ERROR: ", exp<b></b> "It is invalid expression<b></b>.")
       break
       if not operandStack.is_empty():
        y = operandStack.pop()
       else:
       print(" An ERROR: ", exp<b></b> "It is an invalid postfix exp<b></b>.")
      break
else:
operand2 = operandStack.pop() # pop the values of operand2
operand1 = operandStack.pop() # pop the values of operand1
result = doMath(token,operand1,operand2) # by using math function applying on result of operands
operandStack.push(result) #push the result value
return operandStack.pop() # pop the stack value.

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