Pyhton: Calculator Parser

gistfile1.py

import sys

class Number:
    def __init__(self, lexeme):
        self.lexeme = lexeme

class OpenParenthesis:
    lexeme ="("

class CloseParenthesis:
    lexeme = ")"

class Operator:
    def __init__(self, lexeme):
        self.lexeme = lexeme

class WhiteSpace:
    def __init__(self, lexeme):
        self.lexeme = lexeme
    
class Tree:
    def __init__(self, token):
        self.token = token
        self.left = None        
        self.right = None
        
        
    def getValue(self):
        if (isinstance(self.token,Operator)):
            if (self.token.lexeme == "+"):
                return self.left.getValue() + self.right.getValue()   
            elif (self.token.lexeme == "-"):
                return self.left.getValue() - self.right.getValue() 
            elif (self.token.lexeme == "/"):
                if(self.right.getValue()!=0):
                    return self.left.getValue() / self.right.getValue()
                else:
                    print("\nNo existe la division sobre 0")
                    sys.exit()
            elif (self.token.lexeme == "*"):
                return self.left.getValue() * self.right.getValue()  
            else:
                return self.left.getValue() % self.right.getValue()
        elif(isinstance(self.token,Number)):
            return float(self.token.lexeme)
        else:
            print("Token invalido " + str(self.token))
            sys.exit()

        
def toToken(char):
    if(char.isdigit()):
        return Number(char)
    elif(char=='('):
        return OpenParenthesis()  
    elif(char==')'):
        return CloseParenthesis()
    elif(char == '*' or char == '/' or char == '+' or char == '-' or char == '%'):
        return Operator(char)
    elif(char == ' '):
        return WhiteSpace(char)        
    else:
        print("Error en la cadena caracter invalido " + char)
        sys.exit()
        

print sys.argv
string = sys.argv[1]
sizeString = len(string)
listaTokens = []
pointer = 0
treeList = []

for i in range(0,sizeString):
    if(not(isinstance(toToken(string[i]),WhiteSpace))):
        listaTokens.append(toToken(string[i]))    
        
def term(token):
    global pointer , treeList
    if(isinstance(listaTokens[pointer],token)):        
        treeList.append(Tree(listaTokens[pointer]))
        if(isinstance(listaTokens[pointer],CloseParenthesis)):            
            operator = treeList[-4]
            operator.left = treeList[-3]
            operator.right = treeList[-2]        
            del treeList[-5:len(treeList)]
            treeList.append(operator)
        pointer = pointer + 1
        return True
    else:
        return False
 
   
def E():
    global pointer , treeList
    save = pointer
    if(E1()):       
        return True    
    else:
        del treeList[save:len(treeList)] 
        pointer = save
        if(E2()):
            return True
        else:
            del treeList[save:len(treeList)] 
            pointer = save
            if(E3()):
                return True
            else:
                del treeList[save:len(treeList)] 
                pointer = save
                if(E4()):
                    return True
                else:               
                    del treeList[save:len(treeList)]
                    return False

                
        
def E1():
    if(term(OpenParenthesis) and term(Operator) and term(Number) and term(Number) and term(CloseParenthesis)):
        return True
    else:
        return False
    
def E2():
    if(term(OpenParenthesis) and term(Operator) and E() and E() and term(CloseParenthesis)):
        return True
    else:
        return False

def E3():
    if(term(OpenParenthesis) and term(Operator) and term(Number) and E() and term(CloseParenthesis)):
        return True
    else:
        return False
    
def E4():
    if(term(OpenParenthesis) and term(Operator) and E() and term(Number) and term(CloseParenthesis)):
        return True
    else:
        return False
    

print(E())
print treeList[0].getValue()