class Conversion:
# Constructor to initialize the class variables
def __init__(self, capacity):
self.top = -1
self.capacity = capacity
# This array is used a stack
self.array = []
# Precedence setting
self.output = []
self.precedence = {'+': 1, '-': 1, '*': 2, '/': 2, '^': 3}
# Check if the stack is empty
def isEmpty(self):
return True if self.top == -1 else False
# Return the value of the top of the stack
def peek(self):
return self.array[-1]
# Pop the element from the stack
def pop(self):
if not self.isEmpty():
self.top -= 1
return self.array.pop()
else:
return "$"
# Push the element to the stack
def push(self, op):
self.top += 1
self.array.append(op)
# A utility function to check is the given character
# is operand
def isOperand(self, ch):
return ch.isalpha()
# Check if the precedence of operator is strictly
# less than top of stack or not
def notGreater(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 infixToPostfix(self, exp):
# Iterate over the expression for conversion
for i in exp:
# If the character is an operand,
# add it to output
if self.isOperand(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.isEmpty()) and
self.peek() != '('):
a = self.pop()
self.output.append(a)
if (not self.isEmpty() and self.peek() != '('):
return -1
else:
self.pop()
# An operator is encountered
else:
while(not self.isEmpty() and self.notGreater(i)):
self.output.append(self.pop())
self.push(i)
# Pop all the operator from the stack
while not self.isEmpty():
self.output.append(self.pop())
for ch in self.output:
print(ch, end="")
# Driver code
if __name__ == '__main__':
exp = "a+b*(c^d-e)^(f+g*h)-i"
obj = Conversion(len(exp))
# Function call
obj.infixToPostfix(exp)
Infix To Postfix Conversion in Python using stack - Type-1
import sys from collections import deque # Utility function to return precedence of the given operator. # Note that higher is the precedence, lower is its value def prec(c): # Multiplication and division if c == '*' or c == '/': return 3 # Addition and subtraction if c == '+' or c == '-': return 4 # Bitwise AND if c == '&': return 8 # Bitwise XOR (exclusive or) if c == '^': return 9 # Bitwise OR (inclusive or) if c == '|': return 10 # add more operators if needed return sys.maxsize # for opening bracket '(' # Utility function to check if a given token is an operand def isOperand(c): return ('a' <= c <= 'z') or ('A' <= c <= 'Z') or ('0' <= c <= '9') # Function to convert an infix expression to a postfix expression. # This function expects a valid infix expression def infixToPostfix(infix): # base case if not infix or not len(infix): return True # create an empty stack for storing operators s = deque() # create a string to store the postfix expression postfix = '' # process the infix expression from left to right for c in infix: # Case 1. If the current token is an opening bracket '(', push it into # the stack if c == '(': s.append(c) # Case 2. If the current token is a closing bracket ')' elif c == ')': # pop tokens from the stack until the corresponding opening bracket '(' # is removed. Append each operator at the end of the postfix expression while s[-1] != '(': postfix += s.pop() s.pop() # Case 3. If the current token is an operand, append it at the end of the # postfix expression elif isOperand(c): postfix += c # Case 4. If the current token is an operator else: # remove operators from the stack with higher or equal precedence # and append them at the end of the postfix expression while s and prec(c) >= prec(s[-1]): postfix += s.pop() # finally, push the current operator on top of the stack s.append(c) # append any remaining operators in the stack at the end of the postfix expression while s: postfix += s.pop() # return the postfix expression return postfix if __name__ == '__main__': infix = 'A+B*CāD*E' postfix = infixToPostfix(infix) print(postfix)