Programming

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:

Code:

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:

Code:

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- .

Thanks!

Is this a homework assignment?

Homework assignments must be posted in the Homework & Coursework Forum and must include a completely filled out homework template as specified in that forum's rules.

Do not post classroom or homework problems in the main forums. Homework and coursework questions can only be posted in this forum under special homework rules.

Please review the rules, which you agreed to when you registered, if you have not already done so.

More-than-likely, posting homework in the main forums has resulting in a forum infraction. If you did not post homework, please explain the company you work for and the nature of the problem you are working on.

If you did post homework in the main forums, please review the guidelines for posting homework and repost.

Thank You.

The UNIX and Linux Forums.