input: Write a function to calculate the number of days between two dates.
  assert days_between_dates(date(2023, 1, 1), date(2023, 1, 10)) == 9
  assert days_between_dates(date(2023, 1, 1), date(2023, 1, 1)) == 0
  assert days_between_dates(date(2023, 12, 25), date(2024, 1, 1)) == 7
output: from datetime import date
  
  def days_between_dates(date1, date2):
      return (date2 - date1).days