Python3 Code for

from stack_array import Stack

def postfix_eval(input_str):

stack = Stack(30)

#Input argument: a string containing a postfix expression where tokens

# are space separated. Tokens are either operators + - * / ** << >> or numbers(<< is left shift, >> is right shift, ** is exponent) # Returns the result of the expression evaluation. #Raises a PostfixFormatException if:

Invalid token if one of the tokens is neither a valid operand nor a valid operator.

o Insufficient operands if the expression does not contain sufficient operands.

o Too many operands if the expression contains too many operands.

o Illegal bit shift operand if one or more operands to a bit shift operator is a float instead of an int.

o Note: to raise an exception with a message: rasie PostfixFormatException(Here is a message)