python遇到的困难：总是报错EOFError: Ran out of input

# coding=utf-8
import pickle
def usr_date():
try:
with open('usr_date.pkl','rb') as f:
return pickle.load(f)
except EOFError: #捕获异常EOFError 后返回None
return None

def update_usr(usr_dic):
with open('usr_date.pkl','wb') as f:
pickle.dump(usr_dic,f)

def register():
'注册'
usr_dic = {}
usr_name = input('请输入用户名')
open_date = usr_date() if usr_date() else {}
if usr_name in open_date.keys():
print('用户已存在，请登录')
return False
usr_password = input('请输入你的密码：')
usr_dic[usr_name] = usr_password
update_usr(usr_dic)
return print('注册成功')

def Sign_in():
'登录'
pass

def login_index():
while True:
usr = input('1.注册 2.登录 0.退出')
if usr == '1':
register()
elif usr =='2':
Sign_in()
else:
break