input: Write a python function to calculate the number of days between two dates.
  assert calculate_days_between('2023-01-01', '2023-01-10') == 9
  assert calculate_days_between('2023-02-01', '2023-02-28') == 27
  assert calculate_days_between('2022-12-31', '2023-01-01') == 1
output: from datetime import datetime
  
  def calculate_days_between(date1, date2):
      date_format = "%Y-%m-%d"
      d1 = datetime.strptime(date1, date_format)
      d2 = datetime.strptime(date2, date_format)
      delta = d2 - d1
      return delta.days