python实现最简单的计算器功能源码

 import re

 def calc(formula):
     formula = re.sub(' ', '', formula)
     formula_ret = 0
     match_brackets = re.search(r'\([^()]+\)', formula)
     if match_brackets:
         calc_result = calc(match_brackets.group().strip("(,)"))
         formula = formula.replace(match_brackets.group(), str(calc_result))
         return calc(formula)
     else:
         formula = formula.replace('--', '+').replace('++', '+').replace('-+', '-').replace('+-', '-')
         while re.findall(r"[*/]", formula):
             get_formula = re.search(r"[.\d]+[*/]+[-]?[.\d]+", formula)
             if get_formula:
                 get_formula_str = get_formula.group()
                 if get_formula_str.count("*"):
                     formula_list = get_formula_str.split("*")
                     ret = float(formula_list[0]) * float(formula_list[1])
                 else:
                     formula_list = get_formula_str.split("/")
                     ret = float(formula_list[0]) / float(formula_list[1])
                 formula = formula.replace(get_formula_str, str(ret)).replace('--', '+').replace('++', '+')
         formula = re.findall(r'[-]?[.\d]+', formula)
         for num in formula:
             formula_ret += float(num)
     return formula_ret
 # calc_str = input('>>>')
 calc_str = '1-2*((60-30+(-40---5)*(9-2*5/3+7/3*99/4*2998+ 10*568/ 14))-(-4*3)/(16-3*2))'
 print(eval(calc_str))
 formula_result = calc(calc_str)
 print(formula_result)

带基本验证

 import re
 invalid_str_re = re.compile(r'[*/]{3,}|[%]{2,}|\([*/%]+\d+|^[*/%]+\d+|\(+\)+|\d+[-+*/%]+$|\)+\(+|\d+[-+*/%]+\)|\d+\(+')

 def decorate(func):
     def wrapper(formula):
         formula = re.sub(' ', '', formula)
         valid_str = re.findall(r'[-+*/%.()\d]+', formula)
         invalid_str = invalid_str_re.findall(formula)
         if (valid_str and len(valid_str[0]) != len(formula)) or invalid_str:
             return False
         return func(formula)
     return wrapper

 @decorate
 def calc(formula):
     formula = re.sub(' ', '', formula)
     formula_ret = 0
     match_brackets = re.search(r'\([^()]+\)', formula)
     if match_brackets:
         calc_result = calc(match_brackets.group().strip("(,)"))
         formula = formula.replace(match_brackets.group(), str(calc_result))
         return calc(formula)
     else:
         formula = formula.replace('--', '+').replace('++', '+').replace('-+', '-').replace('+-', '-')
         while re.findall(r"[*/]", formula):
             get_formula = re.search(r"[.\d]+[*/]+[-]?[.\d]+", formula)
             if get_formula:
                 get_formula_str = get_formula.group()
                 if get_formula_str.count("*"):
                     formula_list = get_formula_str.split("*")
                     ret = float(formula_list[0]) * float(formula_list[1])
                 else:
                     formula_list = get_formula_str.split("/")
                     ret = float(formula_list[0]) / float(formula_list[1])
                 formula = formula.replace(get_formula_str, str(ret)).replace('--', '+').replace('++', '+')
         formula = re.findall(r'[-]?[.\d]+', formula)
         for num in formula:
             formula_ret += float(num)
     return formula_ret
 # calc_str = input('>>>')
 calc_str = '1-2*((60-30+(-40---5)*(9-2*5/3+7/3*99/4*2998+ 10*568/ 14))-(-4*3)/(16-3*2))'
 formula_result = calc(calc_str)
 print(formula_result)