input: Write a python function to add an event to the calendar and retrieve events for a specific date.
  assert add_and_get_events(Date(2023, 10, 1), "Meeting", "Project discussion") == ["Meeting on 10/1/2023"]
  assert add_and_get_events(Date(2023, 12, 25), "Christmas", "Holiday") == ["Christmas on 12/25/2023"]
  assert add_and_get_events(Date(2023, 10, 1), "Doctor's Appointment", "Annual checkup") == ["Meeting on 10/1/2023", "Doctor's Appointment on 10/1/2023"]
output: class Date:
      def __init__(self, year, month, day):
          self.year = year
          self.month = month
          self.day = day
  
      def __eq__(self, other):
          return self.year == other.year and self.month == other.month and self.day == other.day
  
      def __hash__(self):
          return hash((self.year, self.month, self.day))
  
      def __str__(self):
          return f"{self.month}/{self.day}/{self.year}"
  
  calendar_events = {}
  
  def add_and_get_events(date, event_name, event_desc):
      if date not in calendar_events:
          calendar_events[date] = []
      calendar_events[date].append(f"{event_name} on {date}")
      return calendar_events[date]