Question on unknown error

Hello,

I have the following method:

def subscribe_keyword(userid,subDay =7,KEYWORD_SET=frozenset()):

    try:

...

        sub_datetime = datetime.datetime.now()

        exp_datetime = sub_datetime + timedelta(days=subDay)

print 'time'

However when i try to run my app,

The following error throws at those two lines.

Err: sequence item 0: expected string, int found

Is there something wrong with the module?

Best Regards,

Stanwin Siow