python正则实现计算器功能

本文实例为大家分享了python正则实现计算器功能的具体代码，供大家参考，具体内容如下

# -*- coding: utf-8 -*-
# Author :Gogh
# @Time  :2017/12/4 20:16
# @Email :361910002@qq.com
import re
def operator_update(formula):
# 对formula公式进行 去除空字符，更新运算符处理
formula = formula.replace(" ", "") # 去除空字符
formula = formula.replace("+-", "-")
formula = formula.replace("--", "+")
return formula

def calc_muldiv(formula_list):
'''''
计算公式里面的乘除
:param formula: 列表
:return:
'''
for index, element in enumerate(formula_list):
 if "*" in element or "/" in element:
  operators = re.findall("[*/]", element)
  calc_list = re.split("[*/]", element)
  num = None
  for i, e in enumerate(calc_list):
   if num:
    if operators[i - 1] == "*":
     num *= float(e)
    elif operators[i - 1] == "/":
     num /= float(e)
   else:
    num = float(e)
  formula_list[index] = num
return formula_list

def calc_plumin(operators, num_list):
'''''
计算列表数字的加减
:param operators: 运算符列表
:param num_list: 进行运算的数字列表
:return: 返回计算结果
'''
num = None
for i, e in enumerate(num_list):
 if num:
  if operators[i - 1] == "+":
   num += float(e)
  elif operators[i - 1] == "-":
   num -= float(e)
 else:
  num = float(e)
return num

def merge(plus_minus_operator, multiply_divide_list):
'''''
把列表中这样的形式'2*' '-3*' '5/3*' '4/2'合并到一块
:param formula_list:
:return:
'''
for index, element in enumerate(multiply_divide_list):
 if element.endswith("*") or element.endswith("/"):
  multiply_divide_list[index] = element + plus_minus_operator[index] + multiply_divide_list[index + 1]
  del multiply_divide_list[index + 1]
  del plus_minus_operator[index]
  return merge(plus_minus_operator, multiply_divide_list)
return plus_minus_operator, multiply_divide_list

def bracket_calc(formula):
'''''
对括号最内层的formula公式进行计算
:param formula:
:return:
'''
formula = re.sub("[()]", "", formula) # 去除两边的（）
formula = operator_update(formula)
plus_minus_operator = re.findall("[+-]", formula) # 列表 '+' '-' 运算符
multiply_divide_list = re.split("[+-]", formula) # 列表 有'*' '/'
if multiply_divide_list[0] == "": # multiply_divide_list列表第一个字符为空的话，表示一个数字为负号
 multiply_divide_list[1] = "-" + multiply_divide_list[1]
 del plus_minus_operator[0]
 del multiply_divide_list[0]
res = merge(plus_minus_operator, multiply_divide_list)
plus_minus_operator = res[0] # 列表 '+' '-' 运算符 进行合并处理
multiply_divide_list = res[1]
plus_minus_list = calc_muldiv(multiply_divide_list) # 生成只进行加减运算的列表
res = calc_plumin(plus_minus_operator, plus_minus_list)
return res

def calculate(formula):
'''''计算程序主入口, 主要逻辑是先计算拓号里的值,算出来后再算乘除,再算加减'''
while True:
 formula_depth = re.search("[()]+", formula)
 if formula_depth:
  formula_depth = formula_depth.group()
  res = bracket_calc(formula_depth)
  formula = formula.replace(formula_depth, str(res))
  print("\33[34;1m％s\33[0m" ％ (formula))
 else:
  res = bracket_calc(formula)
  print("\33[31;1m结果:％s\33[0m" ％ (res))
  exit()

if __name__ == '__main__':
formula = "1 - 2 * ( (60-30 +(-9-2- 5-2*-3-5/3-40*4/2-3/5+6*3) * (-9-2-5-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) -(-4*3)/ (16-3*2) )"
calculate(formula)

来源：http://blog.csdn.net/Goghdian/article/details/78791468