简单计算器_python3

lf = '+-*/'
while True:
    try:
        str = input()
        for i in range(4):
            if str.find(lf[i]) > 0:
                a, b = map(float, str.split(lf[i]))
                if lf[i] == '/' and b == 0.0 :
                    print('Wrong!Division by zero!')
                else:
                    print('{:.4f}{}{:.4f}={:.4f}'.format(a, lf[i], b, eval(str)))
                break
            elif i == 3 :
                print('Invalid operation!')
    except EOFError:
        break