input: Write a python function to calculate the difference between two dates in days.
  assert date_diff(datetime.date(2023, 10, 1), datetime.date(2023, 10, 10)) == 9
  assert date_diff(datetime.date(2023, 1, 1), datetime.date(2023, 1, 31)) == 30
  assert date_diff(datetime.date(2022, 12, 25), datetime.date(2023, 1, 1)) == 7
output: import datetime
  
  def date_diff(date1, date2):
      return (date2 - date1).days