python program to convert infix to prefix
""" Author : ITVoyagers (itvoyagers.in) Date :1st November 2019 Description : Program to show use of stack in infix to prefix conversion using python. """ class infix_to_prefix: precedence={'^':5,'*':4,'/':4,'+':3,'-':3,'(':2,')':1} def __init__(self): self.items=[] self.size=-1 def push(self,value): self.items.append(value) self.size+=1 def pop(self): if self.isempty(): return 0 else: self.size-=1 return self.items.pop() def isempty(self): if(self.size==-1): return True else: return False def seek(self): if self.isempty(): return False else: return self.items[self.size] def is0perand(self,i): if i.isalpha() or i in '1234567890': return True else: return False def reverse(self,expr): rev="" for i in expr: if i is '(': i=')' elif i is ')': i='(' rev=i+rev return rev def infixtoprefix (self,expr): prefix="" print('prefix expression after every iteration is:') for i in expr: if(len(expr)%2==0): print("Incorrect infix expr") return False elif(self.is0perand(i)): prefix +=i elif(i in '+-*/^'): while(len(self.items)and self.precedence[i] < self.precedence[self.seek()]): prefix+=self.pop() self.push(i) elif i is '(': self.push(i) elif i is ')': o=self.pop() while o!='(': prefix +=o o=self.pop() print(prefix) #end of for while len(self.items): if(self.seek()=='('): self.pop() else: prefix+=self.pop() print(prefix) return prefix s=infix_to_prefix() expr=input('enter the expression ') rev="" rev=s.reverse(expr) #print(rev) result=s.infixtoprefix(rev) if (result!=False): prefix=s.reverse(result) print("the prefix expr of :",expr,"is",prefix)
