python递归理解图

递归：下一级只能return给自己的上一级。

 import re
 val="9-2*5/3+7/3*99/4*2998+10*568/14"
 val="9-2*5/3+7/3*99/4*2998+10*568/14"
 def chen(arg):
     f = arg
     if "*" in arg or "/" in arg:
         b2_2 = re.search("\d+\.*\d*[*/]+\d+\.*\d*", arg)
         m = b2_2.group()
         k = re.split("([*/])", m, 1)
         kn = k[0] + '\\' + k[1] + k[2]
         if k[1] == '*':
            new_a = float(k[0]) * float(k[2])
            f = re.sub(kn, str(new_a), arg)
            new_z = chen(f)
            return new_z
         elif k[1] == '/':
            new_a = float(k[0]) / float(k[2])
            f = re.sub(kn, str(new_a), arg)
            new_z = chen(f)
            return new_z
     return f
 q=chen(val)
 print (q)
 # for i in q:
 #     print (i)