is not None 判断
列表不为空
list_1 = []
if list_1 is not None:
print('list is not none')
列表为空
list_1 = []
if list_1[0] is None:
print('list_1 is none')
if 列表判断
列表不为空（空列表等于 False）
list_2 = []
if list_2:
print('list_2 is not none')
length列表长度判断
列表为空
list_3 = []
if len(list_3) == 0:
print('list_3 is none')
list_3 = []
if len(list):
print('list_3 is not none')
