input: Write a python function to generate a string representing the calendar for a given year.
  assert show_calendar(2023).startswith("                                2023")
  assert show_calendar(2000).startswith("                                2000")
  assert show_calendar(1999).startswith("                                1999")
output: def show_calendar(year):
      import calendar
      cal = calendar.TextCalendar(calendar.SUNDAY)
      return cal.formatyear(year, 2, 1, 1, 3)