(year)
return y*365 + y//4 - y//100 + y//400
year -> number of days before January 1st of year.
year -> number of days before January 1st of year.
year - > number of days before January 1st of year .
def _days_before_year(year):
    "year -> number of days before January 1st of year."
    y = year - 1
    return y*365 + y//4 - y//100 + y//400
def _days_before_year ( year ) : y = year - 1 return y * 365 + y // 4 - y // 100 + y // 400