拟输出一个日期列表：
file=open("C:/Users/jyz_1/Desktop/新建文本文档.txt")
file=file.read()
lsy=[]
dates=file.split("\n")
for date in dates:
while "-" in date:
p1=date.index('-')#the first -
p2=date.find('-',p1+1)#the second -
month=date[p1+1:p2]
day=date[p2+1:-1]
date_on_x=int(month+day)
lsy=lsy.append(date_on_x)
报错：
Traceback (most recent call last):
File "C:\Users\jyz_1\AppData\Local\Programs\Python\Python37-32\32rx.py", line 26, in <module>
lsy=lsy.append(t)
AttributeError: 'NoneType' object has no attribute 'append'
难道lsy不是列表？
在shell中输入：
>>> lsy=[]
>>> a='2015-1-1'
>>> lsy.append(a)
>>> lsy
['2015-1-1']
结果正常。
百思不得其解，求大神解惑。
