python开发计算器

1 业务需求

1.1 用户输入 1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )等类似公式后，必须自己解析里面的(),+,-,*,/符号和公式(不能调用eval等类似功能偷懒实现)，运算后得出结果，结果必须与真实的计算器所得出的结果一致。

2 业务逻辑

2.1 首先获取用户输入，处理非法字符，处理空格

2.2 匹配括号，找到括号内部计算公式

2.3 先计算乘除，再计算加减

2.4 最后返回结果与eval()相互比较

3 代码实现

 import re

 def calculator(formula_1):
     '''
     此函数为主函数
     :param formula: 传入的是不规则公式字符串
     :return:
     '''
     print(formula_1)
     expression = ''
     for s in formula_1:  # 去除空格
         if s == ' ':
             continue
         expression = expression + s
     while True:  # 寻找括号
         is_match = re.search('\([^()]+\)', expression)
         if is_match:
             match_result = is_match.group()
             content = match_result[1:-1]
             result = judge(formula_2=content)  # 调用函数
             expression = expression.replace(match_result,result[0])
         else:  # b如果匹配为空，即没有括号
             result = judge(formula_2=expression)
             return result[0]

 def judge(formula_2):
     '''
     此函数是先调用乘除
     :param formula_2: 取出括号的字符串类型
     :return: 返回计算乘除后的字符串
     '''
     num_list = re.split('[*/+-]', formula_2)
     operator_list = re.findall('[*/+-]', formula_2)
     for k, i in enumerate(num_list):
         if len(i) == 0:
             num_list[k+1] = operator_list[k] + num_list[k+1]  #
             del num_list[k]
             del operator_list[k]
     result = mul_div(formula_3=num_list, yunsuanfu=operator_list)
     return result

 def mul_div(formula_3, yunsuanfu):
     '''
     此函数计算乘除
     :param formula_3: 数字列表
     :param yunsuanfu: 符号列表
     :return: 计算结果
     '''
     flag = True
     while flag:
         for num, mark in enumerate(yunsuanfu):
             if mark == "*" or mark == '/':
                 if mark == "*":
                     b = float(formula_3[num]) * float(formula_3[num+1])
                     formula_3[num] = str(b)
                     del formula_3[num+1]
                     del yunsuanfu[num]
                     break
                 else:
                     b = float(formula_3[num])/float(formula_3[num+1])
                     formula_3[num] = str(b)
                     del formula_3[num+1]
                     del yunsuanfu[num]
                     break
         else:
             flag = False
             if len(yunsuanfu) == 0:
                 return formula_3
             else:
                 result = add_sub(formula_4=formula_3, yunsuanfu_2=yunsuanfu)
                 return result

 def add_sub(formula_4, yunsuanfu_2):
     '''
     此函数计算加减
     :param formula_4: 数字列表
     :param yunsuanfu_2: 符号列表
     :return: 计算结果
     '''
     flag = True
     while flag:
         for num, mark in enumerate(yunsuanfu_2):
             if mark == '+' or mark == '-':
                 if mark == '+':
                     b = float(formula_4[num]) + float(formula_4[num+1])
                     formula_4[num] = str(b)
                     del formula_4[num+1]
                     del yunsuanfu_2[num]
                     break
                 else:
                     b = float(formula_4[num]) - float(formula_4[num + 1])
                     formula_4[num] = str(b)
                     del formula_4[num + 1]
                     del yunsuanfu_2[num]
                     break
         else:  # 使用break不执行此表达式
             flag = False
             return formula_4

 string = "1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) ) "
 result = calculator(string)
 print(result)
 print('-----------------')
 print(eval(string))

4 思路来源

http://www.cnblogs.com/WuYongQi/p/5520592.html