input: Write a python function to calculate the difference in days between two dates.
  assert date_difference(datetime.date(2023, 10, 1), datetime.date(2023, 10, 5)) == 4
  assert date_difference(datetime.date(2022, 1, 1), datetime.date(2022, 1, 1)) == 0
  assert date_difference(datetime.date(2020, 1, 1), datetime.date(2021, 1, 1)) == 366
output: import datetime
  
  def date_difference(date1, date2):
      return abs((date2 - date1).days)