I am using V14 and am trying to calculate the duration.   I am using the following formula but it keeps returning a value of 0

for record in self:

    dateDueString = str(record.x_studio_pickup)

    dateMonthString = str(record.x_studio_invoice_date)

    try:

      dateDue = datetime.datetime.strptime( dateDueString, '%Y-%m-%d' )

      dateMonth = datetime.datetime.strptime( dateDueString, '%Y-%m-%d' )

      timeDifference = dateMonth-dateDue

      record['x_studio_duration'] = timeDifference.days

    except:

      record['x_studio_duration']=100000

Can someone tell me the error in my formula?