Create Infix_Postfix.py

Author: ujjwalshiva

python/Infix_Postfix.py

@@ -0,0 +1,101 @@
+class stack:
+    def __init__(self):
+        self.item = []
+    
+    def push(self,it):
+        self.item.append(it)
+    def peek(self): #position of the data
+        if self.isempty() == True:
+            return 0
+        return self.item[-1]
+    
+    def pop(self):
+        if self.isempty() == True:
+            return 0
+        return(self.item.pop())
+    
+    def length(self):
+        return (len(self.item))
+    
+    
+    def isempty(self):
+        if self.item == []:
+            return True
+        else:
+            return False
+    
+    def display(self):
+        if self.isempty()== True:
+            return
+        temps = stack()
+        while(self.isempty() != True):
+            x = self.peek()
+            print("~",x)
+            temps.push(x)
+            self.pop()
+        while(temps.isempty() != True):
+            x = temps.peek()
+            self.push(x)
+            temps.pop()
+    
+    
+    def isOperand(self, ch): 
+        return ch.isalpha()
+        
+    def notGreater(self, i):
+        precedence = {'+':1, '-':1, '*':2, '/':2, '%':2, '^':3}
+        if self.peek() == '(':
+            return False
+        a = precedence[i]
+        b = precedence[self.peek()] 
+        if a <= b:
+            return True
+        else:
+            return False
+            
+    
+    
+    def infixToPostfix(self, exp):
+        output = ""
+        
+        for i in exp:
+            
+            if self.isOperand(i) == True: # check if operand add to output
+                print(i,"~ Operand push to stack")
+                output = output + i
+    
+            # If the character is an '(', push it to stack 
+            elif i == '(':
+                self.push(i)
+                print(i," ~ Found ( push into stack")
+    
+            elif i == ')': # if ')' pop till '('
+                while( self.isempty() != True and self.peek() != '('):
+                    n = self.pop() 
+                    output = output + n
+                    print(n, "~ Operator popped from stack")
+                if (self.isempty() != True and self.peek() != '('):
+                    print("_________")
+                    return -1
+                else:
+                    x = self.pop()
+                    print(x, "Popping and deleting (")
+            else: 
+                while(self.isempty() != True and self.notGreater(i)):
+                    if self.peek()=='^' and i=='^':
+                        break
+                    c = self.pop()
+                    output = output + c
+                    print(c,"Operator popped after checking precedence from stack")
+                self.push(i)
+                print(i,"~ Operator pushed to stack")
+    
+        # pop all the operator from the stack 
+        while self.isempty() != True:
+            xx = self.pop()
+            output = output + xx
+            print(xx,"~ pop at last")
+        print(output)
+        self.display()
+st = stack()
+st.infixToPostfix("a^b^c")