I am trying to get a datetime seven days prior to another date.
So I am doing in the console:
import datetime
from dateutil.relativedelta import relativedelta
dt = datetime.date(2014, 10, 18)
dt_minus_one_week = datetime.date(2014, 10, 18) - relativedelta(days=7)
The result is, as expected, datetime.date(2014, 10, 11). However, I am running a webservice (using eve, but I think that this is unimportant) application for a long time, and then when I invoke the method to get the one week older date, I get datetime.date(2014, 10, 10). The code is exactly the same as above.
If I restart the app, the date is what I expected it to be. Why is this happening? Is relativedelta nondeterministic? Is there any way to "reset" it so I can get the right value again?
From the description of your functions in the comments, you have stepped on a common python "landmine".
def get_d_minus_one_pacific_local_date():
return datetime.datetime.now(
pytz.timezone('US/Pacific')).date() - relativedelta(days=1)
def get_relative_date(init=get_d_minus_one_pacific_local_date(), *args, **kwargs):
return init + datetime.timedelta(*args, **kwargs)
# ...
get_relative_date(days=-7)
When you set the default value of init in get_relative_date definition, it will not be recalculated again. So when the next day comes, it will use the value obtained at the time of function definition.