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)