exe_131_infix_to_postfix.py

"""
The program receives a MATHEMATICAL EXPRESSION from the USER
and return the same expression EXPRESSED in POSTFIX FORM (RPN).
"""


# START Definition of the FUNCTIONS


def checkEntry(math_exp):      # possible evolution -> check entry
    pass


def tokenizingString(string):       # possible evolution -> import
    # LIST of the MATHEMATICAL OPERATORS
    tokens = ["+", "-", "*", "/", "^", "(", ")"]
    tokens_list = []
    i = 0
    while i < len(string):
        # Check MATHEMATICAL OPERATORS
        if string[i] in tokens:
            tokens_list.append(string[i])
        # Check INTEGERS
        elif string[i].isdigit():
            tmp = ""
            # LOOP for NUMBERS > 1 DIGITS
            while i < len(string):
                if string[i].isdigit():
                    tmp += string[i]
                    i += 1
                else:
                    i -= 1
                    break
            tokens_list.append(tmp)
        i += 1
    return tokens_list      # RETURN LIST of TOKENS


def operatorUnaryBinary(original_tokens_list):      # possible evolution -> import
    tokens_list = original_tokens_list[:]   # copy list
    operators = ["+", "-"]
    if tokens_list[0] in operators:
        # duplicates accepted
        tokens_list[0] = "u" + tokens_list[0]
    for i in range(1, len(tokens_list)):
        if tokens_list[i] in operators and tokens_list[i-1] == "(":
            # duplicates accepted
            tokens_list[i] = "u" + tokens_list[i]
    return tokens_list


def operatorPrecedence(operator):      # fuction updated
    if (operator == "+" or operator == "-"):
        return 1
    elif (operator == "*" or operator == "/"):
        return 2
    elif (operator == "u+" or operator == "u-"):
        return 3
    elif (operator == "^"):
        return 4


def infixToPostfix(list_infix_expression):
    token_operators = ["+", "u+", "-", "u-",
                       "*", "/", "^"]  # without parentheses
    operators = []
    postfix = []
    for token in list_infix_expression:
        # CHECK INTEGER
        if token.isdigit():
            postfix.append(token)
        # CHECK OPERATORS
        if token in token_operators:
            while operators != [] and operators[-1] != "(" and \
                    operatorPrecedence(token) <= operatorPrecedence(operators[-1]):
                postfix.append(operators.pop())
            operators.append(token)
        # CHECK PARENTHESES
        if token == "(":
            operators.append(token)
        if token == ")":
            while operators[-1] != "(":
                postfix.append(operators.pop())
            operators.remove("(")
    while operators != []:
        postfix.append(operators.pop())
    return postfix


# END Definition of FUNCTIONS


# START MAIN PROGRAM
def main():

    # Acquisition of DATA entered by the USER
    math_exp = input("Enter the MATHEMATICAL EXPRESSION: ")
    # STRING TESTING
    # math_exp = "-1*(-2 + (6 * (3-1)) / 844 + (74 - (-3)) / 121-10+10"

    # Generation of the TOKENS LIST
    tokens_list = tokenizingString(math_exp)

    # Generation of the TOKENS LIST with the identification of UNARY and BINARY operators
    tokens_list_updated = operatorUnaryBinary(tokens_list)

    # Generation of the POSTFIX LIST
    postfix_expression = infixToPostfix(tokens_list_updated)

    # Displaying the EXPRESSIONS
    print("ORIGINAL EXPRESSION -> {}".format(math_exp))
    print("POSTFIX EXPRESSION -> ", end="")
    for token in postfix_expression:
        print(token, end=" ")


if __name__ == "__main__":
    main()