Question

Write a program to convert a text-file containing expressions (one per line) into post-fix expressions outputted to a file of your choice using a stack with one space between operators and variables (one letter variables) and/or constants (one digit constants). IN PYTHON please

Answer 1

SOURCE CODE:

*Please follow the comments to better understand the code.

**Please look at the Screenshot below and use this code to copy-paste.

***The code in the below screenshot is neatly indented for better understanding.


class Conversion:

    # Constructor to initialize the class variables 
    def __init__(self, capacity):
        self.top = -1
        self.capacity = capacity
        # This stack is used a stack 
        self.stack = []
        # Precedence setting 
        self.output = []
        self.precedence = {'+': 1, '-': 1, '*': 2, '/': 2, '^': 3}

    # Pop the element from the stack
    def pop(self):
        if not self.is_empty():
            self.top -= 1
            return self.stack.pop()
        else:
            return "$"

    # Push the element to the stack 
    def push(self, op):
        self.top += 1
        self.stack.append(op)

        # Return the value of the top of the stack

    def peek(self):
        return self.stack[-1]

    # Check if the precedence of operator is
    # less than top of stack
    def not_greater(self, i):
        try:
            a = self.precedence[i]
            b = self.precedence[self.peek()]
            return True if a <= b else False
        except KeyError:
            return False

    # The main function that converts given infix expression 
    # to postfix expression 
    def infix_to_postfix(self, exp):

        # Iterate over the expression for conversion 
        for i in exp:
            # If the character is an operand, 
            # add it to output 
            if self.is_operand(i):
                self.output.append(i)

            # If the character is an '(', push it to stack 
            elif i == '(':
                self.push(i)

            # If the scanned character is an ')', pop and 
            # output from the stack until and '(' is found 
            elif i == ')':
                while (not self.is_empty()) and self.peek() != '(':
                    a = self.pop()
                    self.output.append(a)
                if not self.is_empty() and self.peek() != '(':
                    return -1
                else:
                    self.pop()

                # OPERAND HERE
            else:
                while not self.is_empty() and self.not_greater(i):
                    self.output.append(self.pop())
                self.push(i)

            # pop all the operator from the stack 
        while not self.is_empty():
            self.output.append(self.pop())
        # return as a string
        return " ".join(self.output)

        # check if the stack is empty

    def is_empty(self):
        return True if self.top == -1 else False

    def is_operand(self, ch):
        return ch.isalpha()

def main():
    # READ THE FILE LINE BY LINE
    with open('test.txt') as file:
        for line in file.readlines():
            # REPLACE THE SPACES FOR OUR CONVINIENCE
            line = line.replace(' ', '')

            # If the last character is \n. remove it
            if line[-1] == '\n':
                line = line[:-1]

            # Create an object
            obj = Conversion(len(line))

            # call the method on the string
            post_fix = obj.infix_to_postfix(line)
            print(post_fix)


if __name__ == '__main__':
    main()

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SCREENSHOT:

OUTPUT: