Converting date to number of days in Julian Calendar

dateToJND.py

# Converting date to number of days
# Useful when you need to add few days and get a date
# https://en.wikipedia.org/wiki/Julian_day
def toJND(day,month,year):
	a = (14-month)//12
	y = year + 4800 - a
	m = month + 12*a - 3

	return day + (153*m+2)//5 + 365*y + y//4 - 32083

def fromJND(JND):
	e = 4*(JND + 1401) + 3
	h = 5*((e%1461) // 4) + 2
	day = (h % 153) // 5 + 1
	month = (h // 153 + 2) % 12 + 1
	year = e//1461 - 4716 + (12+2-month)//12

	return (day, month, year)

print(fromJND(toJND(30,4,2009)+366))
# 1 5 2010