code: def julian_day(year, month=1, day=1):
      
      janfeb = month < 3
      return (day
              + 1461 * (year + 4800 - janfeb) // 4
              + 367 * (month - 2 + janfeb * 12) // 12
              - 3 * ((year + 4900 - janfeb) // 100) // 4
              - 32075)
docs: Given a proleptic Gregorian calendar date, return a Julian day int.