Python - 为分数执行字符串代码

Question

我一直在使用 from fractions import * 按照以下逻辑使用某种类型的分数计算器:

a = Fraction(1,4)
b = Fraction(2,5)
c = Fraction(3,4)

print(a+b*c)

输出

11/20

但我需要从字符串中执行语句，就像 1/4 + 1/2 并且出于某种原因总是返回我 0 或 1 :

from fractions import *

class main():
    for i in range(0, 10):
        print "\t\nWRITE YOUR OPERATION"
        code = 'print('
        s = raw_input()
        elements = s.split()

        for element in elements:
            print(element)

            if '/' in element:
                fraction = element.split('/')
                numerator = fraction[0]
                denominator = fraction[1]
                a = Fraction(int(numerator),int(denominator))
                code = code + str(a)
            else:
                code = code + str(element)                

        code = code + ')'        

        exec code

这是我想念的东西吗？

编辑 1

我知道这里出了什么问题

字符串代码是这样的:

code = 'print(1/4+2/5*3/4)'

但我真正需要的是这个(我认为这是不可能的):

code = 'print(Fraction(1,4)+Fraction(2,5)*Fraction(3,4))'

或者有办法做这样的事情......？

Answer 1

我试过了，这是有效的(我的输入是 a/b + c/d 的形式):

from fractions import*

print ("your operation:")

op = input()
#print (op)

elements = op.split()

for el in elements:
    if ('/' in el):
       fraction = el.split('/')
       numerator = fraction[0]
       denominator = fraction[1]

       a = Fraction(int(numerator),int(denominator))

    print (numerator)
    print (denominator)
    print (a)