利用正则表达式来实现求一个数学表达式的和

 1 import re
 2 # formula = "1-2*((60-30+(-40.0/5)*(9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2))"
 3 #  #含义：匹配括号，但是不匹配成对的括号，按正则表达式进行分割，最大分割次数为1次,取出最内层的括号内的一组元素
 4 # val = re.split(‘\(([^()]+)\)‘,formula,1)
 5 # before,center,last=val
 6 # print(val)
 7 # #将取出的内容进行运算
 8 # if "*" in center:
 9 #     new_center=re.split("\*",center)
10 #     sub_res=float(new_center[0])*float(new_center[1])
11 #     print("单步计算结果为：",sub_res)
12 #
13 # elif "/" in center:
14 #     new_center=re.split("/",center)
15 #     sub_res=float(new_center[0])/float(new_center[1])
16 #     print("单步计算结果为：",sub_res)
17 #
18 # formula=before+str(sub_res)+last
19 # print(formula)
20 # val1 = re.split(‘\(([^()]+)\)‘,formula,1)
21 # print(val1)
22 # val2= re.split(‘(\d+\.?\d*[*/][\-]?\d+\.?\d*)‘,formula,1)
23 # print("val2:",val2)
24 # before1,center1,last1=val2
25 #
26 # if "*" in center1:
27 #     new_center=re.split("\*",center1)
28 #     print("111:",new_center)
29 #     sub_res=float(new_center[0])*float(new_center[1])
30 #     print("单步计算结果为：",sub_res)
31 #
32 # elif "/" in center1:
33 #     new_center=re.split("/",center1)
34 #     sub_res=float(new_center[0])/float(new_center[1])
35 #     print("单步计算结果为：",sub_res)
36 
37 
38 
39 
40 
41 #计算，首先利用正则表达式，匹配最内层括号，并取出最内层括号内的元素，然后进行最内层括号内运算
42 def calc(formula):
43     while True:
44         #取最里层括号里面的内容，进行运算
45         val =re.split(‘\(([^()]+)\)‘,formula,1)
46         if len(val)==3:
47             before,center,last=val
48             new_center=mul_div(center)
49             formula=before+str(new_center)+last
50         else:
51             return mul_div(formula)
52 
53 def mul_div(formula):
54     while True:
55         #取优先级高的，进行拆分计算
56         val1=re.split(‘(\d+\.?\d*[*/][\-]?\d+\.?\d*)‘,formula,1)
57         if len(val1)==3:
58             bef,cent,la=val1
59             if "*" in cent:
60                 new_cent=re.split("\*",cent)
61                 sub_res=float(new_cent[0])*float(new_cent[1])
62                 formula=bef+str(sub_res)+la
63             elif "/" in cent:
64                 new_cent=re.split("/",cent)
65                 sub_res=float(new_cent[0])*float(new_cent[1])
66                 formula=bef+str(sub_res)+la
67         else:
68             return final(formula)
69 
70 def final(formula):
71     #由前面的分析结果可以看出，拆分时运算符被拆分，但计算结果有时含有运算符，故需进行替换
72     formula = formula.replace(‘++‘,‘+‘).replace(‘+-‘,‘-‘).replace(‘-+‘,‘-‘).replace(‘--‘,‘+‘)
73     num = re.findall(‘[+\-]?\d+\.?\d*‘,formula)
74     total = 0
75     for i in num:
76         total += float(i)
77     return total
78 
79 
80 
81 if __name__ == ‘__main__‘:
82     formula = "1-2*((60-30+(-40.0/5)*(9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2))"
83     result=calc(formula)
84     print(result)