python实现最简单的计算器功能源码

 1 import re
 2
 3
 4 def calc(formula):
 5     formula = re.sub(‘ ‘, ‘‘, formula)
 6     formula_ret = 0
 7     match_brackets = re.search(r‘\([^()]+\)‘, formula)
 8     if match_brackets:
 9         calc_result = calc(match_brackets.group().strip("(,)"))
10         formula = formula.replace(match_brackets.group(), str(calc_result))
11         return calc(formula)
12     else:
13         formula = formula.replace(‘--‘, ‘+‘).replace(‘++‘, ‘+‘).replace(‘-+‘, ‘-‘).replace(‘+-‘, ‘-‘)
14         while re.findall(r"[*/]", formula):
15             get_formula = re.search(r"[.\d]+[*/]+[-]?[.\d]+", formula)
16             if get_formula:
17                 get_formula_str = get_formula.group()
18                 if get_formula_str.count("*"):
19                     formula_list = get_formula_str.split("*")
20                     ret = float(formula_list[0]) * float(formula_list[1])
21                 else:
22                     formula_list = get_formula_str.split("/")
23                     ret = float(formula_list[0]) / float(formula_list[1])
24                 formula = formula.replace(get_formula_str, str(ret)).replace(‘--‘, ‘+‘).replace(‘++‘, ‘+‘)
25         formula = re.findall(r‘[-]?[.\d]+‘, formula)
26         for num in formula:
27             formula_ret += float(num)
28     return formula_ret
29 # calc_str = input(‘>>>‘)
30 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))‘
31 print(eval(calc_str))
32 formula_result = calc(calc_str)
33 print(formula_result)

带基本验证

 1 import re
 2 invalid_str_re = re.compile(r‘[*/]{3,}|[%]{2,}|\([*/%]+\d+|^[*/%]+\d+|\(+\)+|\d+[-+*/%]+$|\)+\(+|\d+[-+*/%]+\)|\d+\(+‘)
 3
 4
 5 def decorate(func):
 6     def wrapper(formula):
 7         formula = re.sub(‘ ‘, ‘‘, formula)
 8         valid_str = re.findall(r‘[-+*/%.()\d]+‘, formula)
 9         invalid_str = invalid_str_re.findall(formula)
10         if (valid_str and len(valid_str[0]) != len(formula)) or invalid_str:
11             return False
12         return func(formula)
13     return wrapper
14
15
16 @decorate
17 def calc(formula):
18     formula = re.sub(‘ ‘, ‘‘, formula)
19     formula_ret = 0
20     match_brackets = re.search(r‘\([^()]+\)‘, formula)
21     if match_brackets:
22         calc_result = calc(match_brackets.group().strip("(,)"))
23         formula = formula.replace(match_brackets.group(), str(calc_result))
24         return calc(formula)
25     else:
26         formula = formula.replace(‘--‘, ‘+‘).replace(‘++‘, ‘+‘).replace(‘-+‘, ‘-‘).replace(‘+-‘, ‘-‘)
27         while re.findall(r"[*/]", formula):
28             get_formula = re.search(r"[.\d]+[*/]+[-]?[.\d]+", formula)
29             if get_formula:
30                 get_formula_str = get_formula.group()
31                 if get_formula_str.count("*"):
32                     formula_list = get_formula_str.split("*")
33                     ret = float(formula_list[0]) * float(formula_list[1])
34                 else:
35                     formula_list = get_formula_str.split("/")
36                     ret = float(formula_list[0]) / float(formula_list[1])
37                 formula = formula.replace(get_formula_str, str(ret)).replace(‘--‘, ‘+‘).replace(‘++‘, ‘+‘)
38         formula = re.findall(r‘[-]?[.\d]+‘, formula)
39         for num in formula:
40             formula_ret += float(num)
41     return formula_ret
42 # calc_str = input(‘>>>‘)
43 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))‘
44 formula_result = calc(calc_str)
45 print(formula_result)