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)
来源：https://www.cnblogs.com/zengchunyun/p/6194140.html