前序算数表达式

#!/usr/bin/python
#coding=utf-8

import sys
sys.path.append('/home/administrator/python_dir/tools')
from Stack import Stack

num_stack = Stack()
operator_stack = Stack()
brackets_stack = Stack()

import char_tools
def execute_express(press):
    i=0;
    while i < len(press):
        char = press[i]
        if char_tools.str_is_number(press[i]):
           j=exe_num(press,i)
           if j > i and j != -1:
              num_stack.push(press[i:j])
              i=j
           else:
              num_stack.push(press[i])
              i = i+1

        elif char_tools.str_is_operator(press[i]):
           operator_stack.push(press[i])
           i = i+1
        elif press[i] == '(':
           brackets_stack.push(press[i])
           i = i+1
        elif press[i] == ')':
           if brackets_stack.isEmpty() or operator_stack.isEmpty():
              print '有错误'
              raise RuntimeError('有错误')
           else:
              value = exe_num_value(num_stack.pop(),num_stack.pop(),operator_stack.pop())
              num_stack.push(value)
              i = i+1
        else:
           i = i+1

def exe_num_value(num0,num1,operator):
    value = None
    if operator == '+':
       value = int(num0)+int(num1)
    elif operator == '-':
       value = int(num1)-int(num0)
    elif operator == '*':
       value = int(num1)*int(num0)
    elif operator == '/':
       value = int(num1)/int(num0)
    else :
       print '出现错误!\t\n'
       raise RuntimeError('有错误')
    return value

def exe_num(press,i):
   
    while i <len(press):
        if char_tools.str_is_number(press[i]):
           i = i+1
           continue
        else:
           return i
       
    return -1
         

if  __name__ == '__main__':
   

    print '算数表达式计算'
    execute_express('((*2 2)+(+ 1 2 ))')
    print num_stack.pop()