Update 10_Infix_to_Postfix.py

Basic Python Pratice Program/10_Infix_to_Postfix.py

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+# Python program to convert infix expression to postfix
+
+# Class to convert the expression
+
+
+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())
+
+		print "".join(self.output)
+
+
+# Driver's code
+if __name__ == '__main__':
+	exp = "a+b*(c^d-e)^(f+g*h)-i"
+	obj = Conversion(len(exp))
+
+	# Function call
+	obj.infixToPostfix(exp)
+
+# This code is contributed by Shubhanshu kushwaha [Shubhanshu-1507](https://github.com/Shubhanshu-1507)