列表转字符串，再转回来，完全一致
代码：
list1 = [1.0,2.0,3.0]
str = ','.join(str(i) for i in list1)
print('str:', str)
list2 = str.split(',')
print("list2", list2)
list3 = []
for i in list2:
i = float(i)
list3.append(i)
print('list3:', list3)
效果：
str: 1.0,2.0,3.0
list2 ['1.0', '2.0', '3.0']
list3: [1.0, 2.0, 3.0]
